fix: correct housekeeping module bugs after merge

- Restore migration order: remove spurious v30 birthday-reminders entry
  inserted before CardDAV (v30) and birthday-reminders (v31), which caused
  a duplicate v31 on fresh installs
- Restore birthdayReminderAt() offsetMin handling (regression from merge)
- Fix check-in INSERT: check_out was set to checkIn instead of NULL,
  making sessions invisible to loadOpenSession (IS NULL query)
- Implement check-out path in toggleSession() — only check-in was reachable
- Wrap GET /task-templates in try/catch per project convention
- Fix DELETE response envelopes: { ok: true } → { data: ... }
- Remove housekeeping worker exclusion from GET /auth/users
- Replace toISOString() with local-date helper to avoid UTC date shift
- Use user currency preference in money() instead of hardcoded BRL
- Replace hardcoded #7C3AED fallbacks in style attrs with CSS token
- Add German translations for documents folder and settings housekeeping keys
- Remove DESIGN.md and IMPLEMENTATION.md (AI planning artifacts)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/db.js

@@ -1076,15 +1076,6 @@ const MIGRATIONS = [
   },
   {
     version: 30,
-    description: 'Advanced reminder options for birthdays',
-    up: `
-      ALTER TABLE birthdays ADD COLUMN reminder_offset TEXT;
-      ALTER TABLE birthdays ADD COLUMN reminder_custom_amount INTEGER;
-      ALTER TABLE birthdays ADD COLUMN reminder_custom_unit TEXT;
-    `,
-  },
-  {
-    version: 31,
     description: 'CardDAV multi-account contacts sync',
     up: `
       -- ========================================