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/sync/mutationQueue.ts

@@ -73,12 +73,14 @@ export const mutationQueue = {
     if (_flushing || !navigator.onLine) return
     _flushing = true
     try {
-      const pending = await offlineDb.mutationQueue
-        .where('status')
-        .equals('pending')
-        .sortBy('createdAt')
+      while (true) {
+        const pending = await offlineDb.mutationQueue
+          .where('status')
+          .equals('pending')
+          .sortBy('createdAt')
+        const mutation = pending[0]
+        if (!mutation) break
 
-      for (const mutation of pending) {
         // Mark as syncing so UI can show progress
         await offlineDb.mutationQueue.update(mutation.id, { status: 'syncing' })