feat: always-optimistic write pattern across all repos

All create/update/delete repo methods now write to IndexedDB optimistically
and fire mutationQueue.flush() as fire-and-forget, returning immediately
without waiting for the network. This eliminates the 8-second UX freeze
previously seen when the API was unreachable but navigator.onLine was true.

- Repos rewritten: trip, day, place, packing, todo, budget, accommodation,
  reservation, file — write methods never throw, always return optimistic data
- mutationQueue.flush() changed to iterative (one item per loop iteration)
  so mutations enqueued mid-flush (e.g. bulk check-all) are picked up
- fileRepo.toggleStar skips the IDB put when the file is not cached locally
- DayDetailPanel passes place_name into accommodationRepo.create so the
  optimistic accommodation renders the correct hotel label immediately
- Test suite updated throughout to reflect optimistic-first semantics:
  no more rollback assertions, IDB cleared in component test beforeEach hooks,
  FileManager tests switched from filesApi spy to MSW endpoint assertions

client/src/components/Planner/DayDetailPanel.test.tsx

@@ -11,6 +11,7 @@ import { usePermissionsStore } from '../../store/permissionsStore';
 import { resetAllStores, seedStore } from '../../../tests/helpers/store';
 import { buildUser, buildAdmin, buildTrip, buildDay, buildPlace, buildReservation } from '../../../tests/helpers/factories';
 import DayDetailPanel from './DayDetailPanel';
+import { offlineDb } from '../../db/offlineDb';
 
 const day = buildDay({ id: 1, trip_id: 1, date: '2025-06-15', title: 'Day in Paris' });
 
@@ -28,7 +29,9 @@ const defaultProps = {
   onAccommodationChange: vi.fn(),
 };
 
-beforeEach(() => {
+beforeEach(async () => {
+  await new Promise<void>(resolve => setTimeout(resolve, 0));
+  await Promise.all(offlineDb.tables.map(t => t.clear()));
   resetAllStores();
   vi.clearAllMocks();
   server.use(