# Oikos - Product Specification

Self-hosted family planner web app for a single household (2–6 people). No app store, no public access. Deployment via Docker on a private Linux server behind an Nginx reverse proxy with SSL.

---

## Data Model

Every table: `id INTEGER PRIMARY KEY`, `created_at TEXT`, `updated_at TEXT` (ISO 8601).

### Users
| Column | Type | Constraint |
|--------|------|-----------|
| username | TEXT | UNIQUE NOT NULL |
| display_name | TEXT | |
| password_hash | TEXT | bcrypt |
| avatar_color | TEXT | HEX color code |
| role | TEXT | 'admin' or 'member' |

### Tasks
| Column | Type | Constraint |
|--------|------|-----------|
| title | TEXT | NOT NULL |
| description | TEXT | |
| category | TEXT | Household, School, Shopping, Repairs, Other |
| priority | TEXT | none (default), low, medium, high, urgent |
| status | TEXT | open, in_progress, done |
| due_date | TEXT | DATE, nullable |
| due_time | TEXT | TIME, nullable |
| assigned_to | INTEGER | FK → Users |
| created_by | INTEGER | FK → Users, NOT NULL |
| is_recurring | INTEGER | 0/1 |
| recurrence_rule | TEXT | iCal RRULE |
| parent_task_id | INTEGER | FK → Tasks (max 2 levels) |

### Shopping Lists
| Column | Type | Constraint |
|--------|------|-----------|
| name | TEXT | NOT NULL (e.g. "Supermarket", "Hardware store") |

### Shopping Items
| Column | Type | Constraint |
|--------|------|-----------|
| list_id | INTEGER | FK → Shopping Lists, NOT NULL |
| name | TEXT | NOT NULL |
| quantity | TEXT | e.g. "500g", "2 pieces" |
| category | TEXT | FK → Shopping Categories (by name) |
| is_checked | INTEGER | 0/1 |
| added_from_meal | INTEGER | FK → Meals, nullable |

### Shopping Categories
Custom, household-wide category list for shopping items. Replaces the old hardcoded category set.

| Column | Type | Constraint |
|--------|------|-----------|
| id | INTEGER | PRIMARY KEY |
| name | TEXT | NOT NULL |
| sort_order | INTEGER | NOT NULL |
| created_at | TEXT | |
| updated_at | TEXT | |

### Meals
| Column | Type | Constraint |
|--------|------|-----------|
| date | TEXT | DATE, NOT NULL |
| meal_type | TEXT | breakfast, lunch, dinner, snack |
| title | TEXT | NOT NULL |
| notes | TEXT | |
| recipe_url | TEXT | nullable, URL to recipe |
| recipe_id | INTEGER | FK → Recipes (ON DELETE SET NULL), nullable |
| created_by | INTEGER | FK → Users, NOT NULL |

### Recipes
Reusable recipe cards that can be pre-filled into meal slots.

| Column | Type | Constraint |
|--------|------|-----------|
| title | TEXT | NOT NULL |
| notes | TEXT | |
| recipe_url | TEXT | nullable |
| created_by | INTEGER | FK → Users (CASCADE delete) |

### Recipe Ingredients
| Column | Type | Constraint |
|--------|------|-----------|
| recipe_id | INTEGER | FK → Recipes (CASCADE delete), NOT NULL |
| name | TEXT | NOT NULL |
| quantity | TEXT | |
| category | TEXT | NOT NULL (default 'Sonstiges') |

### Meal Ingredients
| Column | Type | Constraint |
|--------|------|-----------|
| meal_id | INTEGER | FK → Meals, NOT NULL |
| name | TEXT | NOT NULL |
| quantity | TEXT | |
| on_shopping_list | INTEGER | 0/1 |

### Calendar Events
| Column | Type | Constraint |
|--------|------|-----------|
| title | TEXT | NOT NULL |
| description | TEXT | |
| start_datetime | TEXT | DATETIME, NOT NULL |
| end_datetime | TEXT | DATETIME |
| all_day | INTEGER | 0/1 |
| location | TEXT | |
| color | TEXT | HEX |
| assigned_to | INTEGER | FK → Users |
| created_by | INTEGER | FK → Users, NOT NULL |
| external_calendar_id | TEXT | ID from external calendar |
| external_source | TEXT | local, google, apple, ics |
| recurrence_rule | TEXT | iCal RRULE |
| subscription_id | INTEGER | FK → ICS Subscriptions (CASCADE delete) |
| user_modified | INTEGER | 0/1 — prevents sync overwrite when 1 |
| calendar_ref_id | INTEGER | FK → External Calendars (ON DELETE SET NULL) |

### External Calendars
Display metadata (name, color) for synced Google/Apple calendars. Populated automatically during sync.

| Column | Type | Constraint |
|--------|------|-----------|
| source | TEXT | 'google' or 'apple', NOT NULL |
| external_id | TEXT | Calendar ID from the provider, NOT NULL |
| name | TEXT | Display name from the provider, NOT NULL |
| color | TEXT | Background color from the provider (HEX) |
| UNIQUE | | (source, external_id) |

### Notes
| Column | Type | Constraint |
|--------|------|-----------|
| title | TEXT | nullable |
| content | TEXT | NOT NULL |
| color | TEXT | HEX |
| pinned | INTEGER | 0/1 |
| created_by | INTEGER | FK → Users, NOT NULL |

### Contacts
| Column | Type | Constraint |
|--------|------|-----------|
| name | TEXT | NOT NULL |
| category | TEXT | Doctor, School/Nursery, Authority, Insurance, Tradesperson, Emergency, Other |
| phone | TEXT | |
| email | TEXT | |
| address | TEXT | |
| notes | TEXT | |

### Budget Entries
| Column | Type | Constraint |
|--------|------|-----------|
| title | TEXT | NOT NULL |
| amount | REAL | NOT NULL (positive = income, negative = expense) |
| category | TEXT | Groceries, Rent, Insurance, Transport, Leisure, Clothing, Health, Education, Other |
| date | TEXT | DATE, NOT NULL |
| is_recurring | INTEGER | 0/1 |
| recurrence_rule | TEXT | iCal RRULE |
| recurrence_parent_id | INTEGER | FK → Budget Entries (generated instance points to original) |
| created_by | INTEGER | FK → Users, NOT NULL |

### Budget Recurrence Skipped
Stores instances of a recurring entry deleted by the user so they are not re-generated.

| Column | Type | Constraint |
|--------|------|-----------|
| parent_id | INTEGER | FK → Budget Entries, NOT NULL |
| month | TEXT | YYYY-MM, NOT NULL |
| PRIMARY KEY | | (parent_id, month) |

### ICS Subscriptions
External calendar feeds subscribed by users (read-only, auto-synced).

| Column | Type | Constraint |
|--------|------|-----------|
| name | TEXT | NOT NULL |
| url | TEXT | NOT NULL (https:// or webcal://) |
| color | TEXT | HEX, default #6366f1 |
| shared | INTEGER | 0/1 — visible to all family members when 1 |
| created_by | INTEGER | FK → Users (SET NULL on delete) |
| etag | TEXT | HTTP ETag for conditional fetch |
| last_modified | TEXT | HTTP Last-Modified for conditional fetch |
| last_sync | TEXT | ISO timestamp of last successful sync |
| created_at | TEXT | ISO timestamp |

### Sync Config
Key-value table for OAuth tokens and CalDAV credentials.

| Column | Type | Constraint |
|--------|------|-----------|
| key | TEXT | PRIMARY KEY |
| value | TEXT | NOT NULL |

---

## Modules

### Dashboard (`/`)

Responsive grid: 1 column on mobile, 2 on tablet, 3 on desktop.

**Widgets:**
- Greeting: "Good [morning/afternoon/evening], [Name]" + date
- Weather: OpenWeatherMap proxy, 3-day preview, refresh every 30 min, hide widget on API error
- Upcoming events: next 3–5, color-coded by person
- Urgent tasks: priority urgent/high + due_date ≤48h
- Today's meals: meals for the current day
- Pinboard preview: 2–3 pinned notes
- FAB (quick actions): + Task, + Event, + Shopping list item, + Note

Skeleton loading instead of spinners. Clicking any widget navigates to that module.

### Tasks (`/tasks`)

**Views:**
- List view (default): grouped by category or due date (toggleable), filter: person, priority, status
- Kanban: columns Open → In Progress → Done, drag & drop
- View mode persisted in localStorage; URL parameter `?view=kanban` overrides (useful for tablet kiosk setups)

**Features:**
- CRUD + subtasks (max 2 levels, checkbox list, progress bar)
- Assignment to users (avatar color as indicator)
- Priorities shown visually via color/icon
- Recurring: automatically create next instance on completion
- Mobile swipe: left = done, right = edit
- Badge for overdue tasks

### Shopping Lists (`/shopping`)

- Multiple lists in parallel
- Items: name, category, quantity, checkbox
- Grouping by category (aisle logic)
- Integration with meal plan: "Add ingredients to shopping list" transfers with source reference
- Checked items shown with strikethrough + moved to bottom
- "Clear list" = remove checked items only
- Autocomplete from previous entries (local)
- Mobile swipe: left = check/uncheck, right = delete; × delete button hidden on mobile (swipe takes over)

### Meal Plan (`/meals`)

Weekly view (Mon–Sun), slots: breakfast / lunch / dinner / snack.

- Meal: title + notes + ingredient list
- "→ Shopping list" button: transfer unchecked ingredients of the week to a selected list
- Week navigation forward/back
- Drag & drop between days/slots
- Autocomplete from meal history
- **Recipe integration:** Select a saved recipe from the meal modal to auto-fill title, notes, URL, and ingredients. Scale ingredient quantities by a numeric factor. Save the current meal as a new recipe with one click.
- **Customizable meal visibility:** In Settings, users can toggle which meal types (breakfast, lunch, dinner, snack) are shown in the planner. Stored as household-wide preference in `sync_config` (key: `visible_meal_types`). At least one type must remain active.

### Recipes (`/recipes`)

Reusable recipe cards linked to meal slots.

- CRUD: title, notes, recipe link, per-ingredient category
- Duplicate existing recipes
- "Add to meal plan" navigates to `/meals` with the selected recipe pre-filled in the modal
- REST API: `GET/POST /api/v1/recipes`, `PUT/DELETE /api/v1/recipes/:id` with ingredient sync

### Calendar (`/calendar`)

**Views:** Month (default, dot indicators), Week (hour grid), Day (timeline), Agenda (list).

- CRUD: title, description, start/end, all-day, location, color, assignment
- Color-coding per person
- Recurring via iCal RRULE
- **Google Calendar:** OAuth 2.0, Calendar API v3, two-way sync
- **Apple Calendar:** CalDAV (tsdav), two-way sync
- **ICS Subscriptions:** Subscribe to any public ICS/webcal URL (e.g. public holidays, sports schedules). Per-subscription color, private/shared visibility, manual "Sync now" and automatic sync on the shared interval. RRULE events expanded into a rolling ±6/+12 month window. SSRF-protected (DNS pre-resolution), ETag/Last-Modified conditional fetch, 10 MB limit, 15 s timeout. User-edited events are protected from being overwritten (`user_modified`); a "Reset to original" link restores them.
- **External calendar names & colors:** Google and Apple sync stores each calendar's display name and background color in the `external_calendars` table (migration v14). A colored `event-cal-label` badge appears in event popups, agenda, month, week, and day views when `cal_name` is present.
- **Event location:** Event popup and dashboard display the location field with RFC 5545 backslash-escape normalization (`\n`, `\,`, `\;`, `\\`) via `fmtLocation()` in `public/utils/html.js`.
- Configurable sync interval (default 15 min)
- External events visually distinguishable
- Conflicts: external event wins, local additions are preserved

### Notes (`/notes`)

Masonry grid with colored sticky notes.

- CRUD: title (optional), content, color
- Pin → appears at top + on dashboard
- Creator shown (avatar color)
- Markdown-light: bold, italic, lists (regex-based)
- Full-text search: client-side filter bar, filters instantly by title + content

### Contacts (`/contacts`)

- CRUD with category filter
- Phone: `tel:` link, email: `mailto:` link
- Address: Maps link (Google/Apple via user agent)
- Real-time search filter
- vCard export: each contact downloadable as `.vcf` (`GET /api/v1/contacts/:id/vcard`)
- vCard import: upload file → client-side parser (FN, TEL, EMAIL, ADR, NOTE, CATEGORIES) → create contact

### Login (`/login`)

Unauthenticated users are redirected here. No public registration form - admin creates users via setup wizard (`setup.js`) or Settings.

- Username + password form
- Error display for wrong credentials
- Rate limiting: 5 attempts/min/IP, 15-min lockout
- After successful login: redirect to dashboard

### Settings (`/settings`)

User management and app configuration. Logged-in users only.

- **Profile:** change display name, avatar color, password
- **User management (admin):** create new users, edit/delete existing users, assign roles (admin/member)
- **Calendar integration:** connect/disconnect Google Calendar OAuth, store Apple Calendar (CalDAV) credentials, configure sync interval; manage ICS URL subscriptions (add, delete, sync now, set color and visibility)
- **Weather:** configure OpenWeatherMap location
- **Language:** System (follows `navigator.language`), German, English, Spanish, French, Italian, Swedish, Greek, Russian, Turkish, Chinese - via `oikos-locale-picker` web component; switch without page reload
- **Tab navigation:** Settings is organized in six tabs (General, Meals, Budget, Shopping, Calendar, Account). Sticky tab bar, active tab persists in sessionStorage, Calendar tab auto-activates after OAuth callbacks.
- **App info:** version, license

### Budget (`/budget`)

**Views:**
- Monthly overview: income vs. expenses, balance, bar chart by category (Canvas, no library)
- Transaction list: chronological, filterable

- CRUD: title, amount, category, date
- Recurring entries
- Monthly comparison (current vs. previous month)
- CSV export

---

## Design System

### Colors (CSS Custom Properties)

Source of truth: `public/styles/tokens.css`. Key values (as of v0.20.39):

**Palette rationale:** Warm-tinted neutral scale (`#FAFAF8 → #121211`) anchored by an **Indigo-600 primary** (`#4F46E5`) that harmonises with the Calendar module violet and the secondary accent. Module colors are semantically separated from severity colors — no hue shared without explicit documentation in `tokens.css`.

```css
:root {
  /* Neutral canvas — warm linen/unbleached-paper atmosphere */
  --color-bg:              #F5F4F1;   /* neutral-100 */
  --color-surface:         #FFFFFF;
  --color-border:          #E8E7E2;   /* neutral-200 */
  --color-text-primary:    #1C1C1A;   /* neutral-900, 14.7:1 on bg */
  --color-text-secondary:  #6C6B67;   /* neutral-600, 5.0:1 on white */
  --color-text-tertiary:   #6A6964;   /* 4.61:1 on bg */

  /* Primary accent — Indigo (warm bias, harmonises with Calendar/violet) */
  --color-accent:           #4F46E5;  /* Indigo-600, 4.93:1 on white (AA) */
  --color-accent-hover:     #4338CA;  /* Indigo-700, 7.04:1 (AAA) */
  --color-accent-active:    #3730A3;  /* Indigo-800 */
  --color-accent-deep:      #2E2D82;  /* deep Indigo for gradients/weather */
  --color-accent-secondary: #7C5CFC;  /* violet — logo gradient, same Indigo family */
  --color-accent-light:     #EEF2FF;  /* Indigo-50 */
  --color-accent-subtle:    #E0E7FF;  /* Indigo-100 */
  --color-btn-primary:      #4338CA;  /* Indigo-700, 7.04:1 on white (AAA) */
  --color-btn-primary-hover:#3730A3;

  /* Severity — hue-separated from module colors */
  --color-success:       #15803D;     /* 4.54:1 */
  --color-warning:       #A15C0A;     /* 5.23:1 — Amber, distinct from --module-meals */
  --color-danger:        #B91C1C;     /* Red-700, 6.90:1 (AAA) */
  --color-info:          #0969DA;     /* 4.64:1 */

  /* Module accents — domain-specific, not interchangeable with severity */
  --module-dashboard:  #4F46E5;   /* Indigo — follows primary accent */
  --module-tasks:      #15803D;   /* Green — intentional share with --color-success */
  --module-calendar:   #8250DF;   /* Violet */
  --module-meals:      #C2410C;   /* Orange-700 */
  --module-shopping:   #DB2777;   /* Pink-600 — distinct from Meals/Warning */
  --module-notes:      #CA8A04;   /* Gold, 4.08:1 — icons/large-text only */
  --module-contacts:   #0969DA;   /* Blue — distinct from Indigo primary */
  --module-budget:     #0F766E;   /* Teal-700, 5.11:1 */
  --module-settings:   #6E7781;   /* Neutral grey */

  /* Priority */
  --color-priority-medium: #A16207;  /* Amber-700, 6.3:1 — distinct from Warning+Meals */
  --color-priority-high:   #C2410C;  /* = --module-meals (documented share: "hot") */
  --color-priority-urgent: #B91C1C;  /* = --color-danger (documented share: "destructive") */

  /* Glass layer tokens */
  --glass-bg: rgba(255,255,255,0.72);
  --glass-border: rgba(255,255,255,0.55);
  --blur-md: 16px;
  --radius-glass-button: 9999px;       /* capsule */
  --ease-glass: cubic-bezier(0.34, 1.56, 0.64, 1); /* spring */

  /* Glass Vibrancy tokens (Phase 4) */
  --glass-bg-card: rgba(255,255,255,0.52);
  --glass-bg-card-hover: rgba(255,255,255,0.65);
  --glass-bg-input: rgba(255,255,255,0.48);
  --glass-bg-toolbar: rgba(255,255,255,0.58);
  --glass-tint-strength: 6%;

  /* Glass inset specular highlights */
  --glass-inset-soft:     inset 0 1px 0 rgba(255,255,255,0.18);
  --glass-inset-base:     inset 0 1px 0 rgba(255,255,255,0.20);
  --glass-inset-medium:   inset 0 1px 0 rgba(255,255,255,0.22);
  --glass-inset-elevated: inset 0 1px 0 rgba(255,255,255,0.28);
  --glass-inset-strong:   inset 0 1px 0 rgba(255,255,255,0.32);
}

/* Dark mode — Hue preserved (Indigo-400), only Lightness/Saturation adjusted.
   Private --_name tokens prevent duplication between @media and [data-theme]. */
@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #1A1A18;       /* deep warm */
    --color-surface: #222220;
    --color-border: #2C2C2A;
    --color-text-primary: #F5F4F1;
    --color-text-secondary: #AEADB0;
    --color-accent:            #818CF8;  /* Indigo-400, 6.8:1 on dark surface */
    --color-accent-hover:      #6366F1;  /* Indigo-500 */
    --color-accent-active:     #4F46E5;  /* Indigo-600 — mirrors light primary */
    --color-accent-light:      #2E2D5B;
    --color-accent-subtle:     #252255;
    --color-btn-primary:       #6366F1;  /* 5.5:1 */
    --color-btn-primary-hover: #4F46E5;
    --module-dashboard: #818CF8;
    --module-meals:     #FB923C;  /* Orange-400 */
    --module-shopping:  #F472B6;  /* Pink-400 — mirrors light entanglement */
    --module-budget:    #2DD4BF;  /* Teal-400 */
    --meal-dinner:      #818CF8;
    --glass-bg: rgba(28,28,26,0.75);
    --glass-border: rgba(255,255,255,0.12);
    --glass-bg-card: rgba(38,38,36,0.50);
    --glass-tint-strength: 8%;
  }
}
```

### Typography
- System font stack, headings 600–700
- Body: 16px mobile, 15px desktop, line-height 1.5
- Caption: 13px, `var(--color-text-secondary)`

### Glass Layer (`public/styles/glass.css`)

Additive CSS file loaded globally after `layout.css`. Implements a Liquid Glass design language inspired by Apple's iOS 26 Liquid Glass, adapted for CSS/web:

**Phase 1-3 (Shell + Components + Polish):**
- **Translucent surfaces:** `backdrop-filter: blur()` on bottom nav, sidebar, modal overlay, cards on hover. All blur effects are inside `@supports (backdrop-filter: blur(1px))` for progressive enhancement.
- **Glass tokens:** Section 16 of `tokens.css` defines `--glass-bg*`, `--glass-border*`, `--blur-xs` through `--blur-xl`, `--opacity-glass-*`, `--glass-highlight*`, `--glass-shadow-sm/md/lg`, `--radius-glass-card/inner/chip/button`, `--ease-glass`, `--transition-glass`. Full dark mode overrides.
- **Capsule shapes:** Buttons, FAB, and search inputs use `--radius-glass-button` (pill shape).
- **Spring animations:** Modal entrance (`glass-modal-scale-in` / `glass-sheet-in`), page transitions, and list stagger all use `cubic-bezier(0.34, 1.56, 0.64, 1)` spring easing.
- **FAB attention pulse:** `fab-ring-pulse` keyframe expands a ring around the FAB to signal readiness.
- **Nav auto-hide:** Bottom bar hides on scroll-down, reappears on scroll-up (mobile only, < 1024px, 4 px hysteresis). CSS: `.nav-bottom--hidden { transform: translateY(calc(100% + var(--safe-area-inset-bottom))); }`. JS: `initNavHideOnScroll()` in `router.js`.

**Phase 4 (Vibrancy + Tint):**
- **Deeper glass penetration:** Dashboard widgets, task cards, note items, meal slots, form inputs, toolbars, group toggles, and FAB speed-dial actions all use semi-transparent glass backgrounds (`--glass-bg-card`, 52% opacity) with `backdrop-filter: blur() saturate()` so underlying content shines through.
- **Module tint:** Each glass surface receives a subtle accent color gradient overlay via `::after` pseudo-element using `color-mix(in srgb, var(--module-accent) var(--glass-tint-strength), transparent)`. Strength is 6% in light mode, 8% in dark mode.
- **App vibrancy background:** `app-content` uses a radial gradient with the active module accent at 3% opacity to provide an ambient color base that glass elements refract.
- **Load-order safety:** All Phase 4 glass selectors use parent-scoped specificity (`.dashboard .widget`, `.tasks-page .task-card`, `.meals-page .meal-slot`) to prevent override by on-demand page CSS that loads after `glass.css`.

**Accessibility:** `prefers-reduced-transparency`, `prefers-reduced-motion`, and `prefers-contrast: more` blocks deactivate blur/animation and restore solid fallbacks across all phases.

### Components
- **Cards:** `var(--color-surface)` base, glass vibrancy via `var(--glass-bg-card)` + `backdrop-filter: blur(8px) saturate(180%)` when supported. `var(--radius-md)`, `var(--shadow-sm)`. Module tint overlay via `::after`. Consistent padding `var(--space-4)` (16px) across all modules.
- **Buttons:** Primary = accent + white. Secondary = outline. Min-height 44px. Capsule shape via `--radius-glass-button`. Submit buttons show success (checkmark, 700ms green via `.btn--success`) and error (shake via `.btn--shaking`).
- **Inputs:** `var(--radius-sm)`, 1.5px border, padding 12px 16px. Search inputs use `--radius-glass-button` and `--glass-border-subtle`. `[required]` fields receive validation status on blur (`.form-field--error` / `.form-field--valid`). Enter moves focus to the next field; Enter on the last field triggers submit.
- **FAB (Floating Action Button):** Color follows the module accent token (`--module-accent`) - each module defines its own accent color. Specular inner highlight + attention ring pulse. Hidden when the virtual keyboard is open (`visualViewport.resize`, threshold 75% of window height).
- **Module accent colors:** `--module-accent` is applied on three visual layers - (1) active nav tab (bottom bar + sidebar stripe), (2) toolbar `border-top: 3px`, (3) cards/rows `border-left: 3px`. The active accent is written to `--active-module-accent` on `:root` on every navigation change. Falls back to `--color-accent` for pages without a module context.
- **Navigation:** Bottom tab bar on mobile (Dashboard, Tasks, Calendar, Meals, More), auto-hides on scroll-down. Sidebar on desktop. Both use glass blur surface.
- **Transitions:** Directional slide-X animation on page change (forward = from right, back = from left, 200ms) with spring easing. Respects `prefers-reduced-motion`.
- **Empty states:** Consistent `.empty-state` class across all modules (icon + title + description, centered). Compact variant `.empty-state--compact` for meal slots.
- **Modals:** Centered panel on desktop with glass overlay. On mobile (< 768px) bottom sheet - spring slide-in from below, sheet handle visible, swipe-to-close (> 80px downward). `focusin` scrolls inputs into view when the virtual keyboard is open.
- **List animation:** Staggered spring fade-in on load (`stagger()` from `public/utils/ux.js`) - max 5 elements staggered (30ms gap), rest appear immediately.
- **Vibration:** `vibrate()` from `public/utils/ux.js` - short pulses for light actions (10-40ms), pattern `[30, 50, 30]` for destructive actions (delete). Respects `prefers-reduced-motion`.
- **PWA install prompt:** Appears only after 2 user interactions. Dismiss window 7 days; interaction counter resets after dismiss.
- **PWA offline fallback:** Service worker serves `/offline.html` when the network is unreachable and `index.html` is not cached. Includes a reload button.

### Breakpoints
- Mobile: < 768px (1 column, bottom nav)
- Tablet: 768–1024px (2 columns, bottom nav)
- Desktop: > 1024px (sidebar + content)

---

## Internationalization (i18n)

All UI strings are managed via `public/i18n.js`. No hardcoded text in JS files outside of locale files.

### Architecture

- **Module:** `public/i18n.js` - exports: `initI18n()`, `setLocale()`, `t(key, params?)`, `getLocale()`, `getSupportedLocales()`, `formatDate(date)`, `formatTime(date)`
- **Locale files:** `public/locales/de.json` (reference), `public/locales/en.json`, `public/locales/es.json`, `public/locales/fr.json`, `public/locales/it.json`, `public/locales/sv.json`, `public/locales/el.json`, `public/locales/ru.json`, `public/locales/tr.json`, `public/locales/zh.json`, `public/locales/ja.json`, `public/locales/ar.json`, `public/locales/hi.json`, `public/locales/pt.json` - structure: `{ "module.camelCaseKey": "Value" }`
- **Variables:** `{{variable}}` syntax in translation strings, e.g. `t('tasks.assignedTo', { name: 'Anna' })`
- **Fallback chain:** active locale → German (`de`) → key itself
- **Date format:** `Intl.DateTimeFormat` with current locale - use `formatDate()` and `formatTime()` from `i18n.js`

### Language Detection

1. `localStorage` entry `oikos-locale` (manual selection)
2. `navigator.languages[0]` (browser language)
3. Fallback: `en`

### Supported Languages

| Code | Language | Status |
|------|----------|--------|
| `de` | German | Reference locale (all keys defined here) |
| `en` | English | Full translation |
| `es` | Spanish | Full translation |
| `fr` | French | Full translation (added v0.16.3) |
| `it` | Italian | Full translation (added v0.5.8) |
| `sv` | Swedish | Full translation (added v0.11.3) |
| `el` | Greek | Full translation (added v0.16.3) |
| `ru` | Russian | Full translation (added v0.16.3) |
| `tr` | Turkish | Full translation (added v0.16.3) |
| `zh` | Chinese (Simplified) | Full translation (added v0.16.3) |
| `ja` | Japanese | Full translation (added v0.19.0) |
| `ar` | Arabic | Full translation (added v0.19.0) |
| `hi` | Hindi | Full translation (added v0.19.0) |
| `pt` | Portuguese | Full translation (added v0.19.0) |

### Adding a New Language

1. Create `public/locales/xx.json` (copy of `de.json`, translate)
2. Add `'xx'` to `SUPPORTED_LOCALES` in `public/i18n.js`
3. Add label in `oikos-locale-picker` (`LOCALE_LABELS['xx'] = 'Name'`)

### Locale Switching

`setLocale(locale)` saves the selection, loads the new locale file, and fires the `locale-changed` custom event. All page modules and web components listen to this event and re-render - no page reload required.
