feat(shopping): custom categories - add, rename, delete and reorder (#26)

- New DB table shopping_categories (migration v5) seeds 9 default
  categories with Lucide icons and sort_order
- Backend CRUD routes: GET/POST/PUT/DELETE /shopping/categories
  plus PATCH /shopping/categories/reorder
- Category validation now uses DB instead of hardcoded constant;
  items of deleted category are moved to the next available one
- Frontend shopping page loads categories from API, dropdown and
  grouping reflect custom order dynamically
- Settings -> Shopping section: list categories with up/down buttons,
  click-to-rename, delete with confirmation; add new categories inline
- i18n keys added in de/en/sv/it

public/locales/de.json

@@ -455,6 +455,19 @@
   "settings": {
     "title": "Einstellungen",
     "sectionDesign": "Design",
+    "sectionShopping": "Einkauf",
+    "shoppingCategoriesLabel": "Einkaufskategorien",
+    "shoppingCategoriesHint": "Kategorien hinzufügen, umbenennen, löschen oder sortieren.",
+    "shoppingCategoryPlaceholder": "Neue Kategorie…",
+    "shoppingCategoryRenameHint": "Klicken zum Umbenennen",
+    "shoppingCategoryRenamePrompt": "Neuer Kategoriename:",
+    "shoppingCategoryMoveUp": "Kategorie nach oben",
+    "shoppingCategoryMoveDown": "Kategorie nach unten",
+    "shoppingCategoryDelete": "Kategorie löschen",
+    "shoppingCategoryDeleteConfirm": "Kategorie \"{{name}}\" löschen? Vorhandene Artikel werden der nächsten Kategorie zugeordnet.",
+    "shoppingCategoryAdded": "Kategorie hinzugefügt.",
+    "shoppingCategoryRenamed": "Kategorie umbenannt.",
+    "shoppingCategoryDeleted": "Kategorie gelöscht.",
     "sectionAccount": "Mein Konto",
     "sectionCalendarSync": "Kalender-Synchronisation",
     "sectionFamily": "Familienmitglieder",

public/locales/en.json

@@ -455,6 +455,19 @@
   "settings": {
     "title": "Settings",
     "sectionDesign": "Appearance",
+    "sectionShopping": "Shopping",
+    "shoppingCategoriesLabel": "Shopping Categories",
+    "shoppingCategoriesHint": "Add, rename, delete or reorder categories.",
+    "shoppingCategoryPlaceholder": "New category…",
+    "shoppingCategoryRenameHint": "Click to rename",
+    "shoppingCategoryRenamePrompt": "New category name:",
+    "shoppingCategoryMoveUp": "Move category up",
+    "shoppingCategoryMoveDown": "Move category down",
+    "shoppingCategoryDelete": "Delete category",
+    "shoppingCategoryDeleteConfirm": "Delete category \"{{name}}\"? Existing items will be moved to the next category.",
+    "shoppingCategoryAdded": "Category added.",
+    "shoppingCategoryRenamed": "Category renamed.",
+    "shoppingCategoryDeleted": "Category deleted.",
     "sectionAccount": "My Account",
     "sectionCalendarSync": "Calendar Sync",
     "sectionFamily": "Family Members",

public/locales/it.json

@@ -455,6 +455,19 @@
   "settings": {
     "title": "Impostazioni",
     "sectionDesign": "Aspetto",
+    "sectionShopping": "Spesa",
+    "shoppingCategoriesLabel": "Categorie spesa",
+    "shoppingCategoriesHint": "Aggiungi, rinomina, elimina o riordina le categorie.",
+    "shoppingCategoryPlaceholder": "Nuova categoria…",
+    "shoppingCategoryRenameHint": "Clicca per rinominare",
+    "shoppingCategoryRenamePrompt": "Nuovo nome categoria:",
+    "shoppingCategoryMoveUp": "Sposta categoria su",
+    "shoppingCategoryMoveDown": "Sposta categoria giu",
+    "shoppingCategoryDelete": "Elimina categoria",
+    "shoppingCategoryDeleteConfirm": "Eliminare la categoria \"{{name}}\"? Gli articoli esistenti verranno spostati alla categoria successiva.",
+    "shoppingCategoryAdded": "Categoria aggiunta.",
+    "shoppingCategoryRenamed": "Categoria rinominata.",
+    "shoppingCategoryDeleted": "Categoria eliminata.",
     "sectionAccount": "Il mio account",
     "sectionCalendarSync": "Sincronizzazione calendario",
     "sectionFamily": "Membri della famiglia",

public/locales/sv.json

@@ -455,6 +455,19 @@
   "settings": {
     "title": "Inställningar",
     "sectionDesign": "Utseende",
+    "sectionShopping": "Inköp",
+    "shoppingCategoriesLabel": "Inköpskategorier",
+    "shoppingCategoriesHint": "Lägg till, byt namn, ta bort eller sortera om kategorier.",
+    "shoppingCategoryPlaceholder": "Ny kategori…",
+    "shoppingCategoryRenameHint": "Klicka för att byta namn",
+    "shoppingCategoryRenamePrompt": "Nytt kategorinamn:",
+    "shoppingCategoryMoveUp": "Flytta kategori uppåt",
+    "shoppingCategoryMoveDown": "Flytta kategori nedåt",
+    "shoppingCategoryDelete": "Ta bort kategori",
+    "shoppingCategoryDeleteConfirm": "Ta bort kategorin \"{{name}}\"? Befintliga artiklar flyttas till nästa kategori.",
+    "shoppingCategoryAdded": "Kategori tillagd.",
+    "shoppingCategoryRenamed": "Kategori omdöpt.",
+    "shoppingCategoryDeleted": "Kategori borttagen.",
     "sectionAccount": "Mitt konto",
     "sectionCalendarSync": "Kalendersynkronisering",
     "sectionFamily": "Familjemedlemmar",