fix: recurring event display and AI query improvements

- Use occurrenceStart instead of startTime in getEventsInRange so
  recurring events show their actual occurrence date to the AI
- Add lazy CalDAV sync in ChatService (syncOnce before first DB access)
- Add CaldavService.sync() with internal config check (silent no-op)
- Show German recurrence description (e.g. "Jede Woche") instead of
  generic "Wiederkehrend" in EventCardBase via formatRecurrenceRule()
- Move RepeatType and REPEAT_TYPE_LABELS from editEvent to shared
- Separate calendar overlay useFocusEffect from event loading

apps/server/src/ai/utils/toolExecutor.ts

@@ -234,7 +234,7 @@ export async function executeToolCall(
 
       const eventsText = events
         .map((e) => {
-          const start = new Date(e.startTime);
+          const start = new Date(e.occurrenceStart);
           const recurrenceInfo = e.recurrenceRule ? " (wiederkehrend)" : "";
           return `- ${e.title} (ID: ${e.id}) am ${formatDate(start)} um ${formatTime(start)} Uhr${recurrenceInfo}`;
         })