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/services/birthdays.js

@@ -57,7 +57,8 @@ function getOffsetMinutes(birthday) {
 
 function birthdayReminderAt(birthDate, offsetMin = 0, from = new Date()) {
   const next = nextBirthdayDate(birthDate, from);
-  return `${next}T12:00:00Z`;
+  const baseTime = new Date(`${next}T12:00:00Z`).getTime();
+  return new Date(baseTime - (offsetMin || 0) * 60000).toISOString();
 }
 
 function eventTitle(name) {