feat: complete offline write support with mutation queue + runtime SW cache config

- Add offline CRUD to todoRepo, budgetRepo, reservationRepo, accommodationRepo,
  dayRepo, tripRepo, fileRepo with optimistic Dexie writes and mutation queue
- Wire all store slices (todo, budget, reservations, files, dayNotes, assignments,
  tripStore) through repos for offline-aware writes
- Cover archive/unarchive, file toggleStar/update/delete, assignment create/delete,
  day title/notes update offline paths
- Migrate service worker from generateSW to injectManifest (custom sw.ts) with
  runtime-configurable api-data (7d/500) and map-tiles (30d/1000) cache policies
- Add Settings → Offline cache configuration UI with save/reset and live SW postMessage
- Extend mutationQueue flush to cover all writable Dexie tables

client/src/store/slices/filesSlice.ts

@@ -35,10 +35,12 @@ export const createFilesSlice = (set: SetState, get: GetState): FilesSlice => ({
   },
 
   deleteFile: async (tripId, id) => {
+    const prev = get().files
+    set(state => ({ files: state.files.filter(f => f.id !== id) }))
     try {
-      await filesApi.delete(tripId, id)
-      set(state => ({ files: state.files.filter(f => f.id !== id) }))
+      await fileRepo.delete(tripId, id)
     } catch (err: unknown) {
+      set({ files: prev })
       throw new Error(getApiErrorMessage(err, 'Error deleting file'))
     }
   },