implement event persistence and improve Mongoose TypeScript patterns

- Add event persistence: confirmed events are now saved to MongoDB
- Refactor Mongoose models to use virtuals for id field with IdVirtual interface
- Update repositories to use toJSON() with consistent type casting
- Add more test responses for chat (doctor, birthday, gym, etc.)
- Show event description in ProposedEventCard
- Change mongo-express port to 8083
- Update CLAUDE.md with Mongoose model pattern documentation

apps/client/src/components/ProposedEventCard.tsx

@@ -40,6 +40,11 @@ export const ProposedEventCard = ({
       <Text style={{ color: currentTheme.textSecondary }}>
         {formatDateTime(event?.startTime)}
       </Text>
+      {event?.description && (
+        <Text style={{ color: currentTheme.textSecondary }} className="text-sm mt-1">
+          {event.description}
+        </Text>
+      )}
       {event?.isRecurring && (
         <Text style={{ color: currentTheme.textMuted }} className="text-sm">
           Wiederkehrend