feat(pwa): implement real offline mode with IndexedDB sync

Add genuine offline read/write capability for trips:

- Dexie IndexedDB schema (trips, places, packing, todo, budget,
  reservations, files, mutationQueue, syncMeta, blobCache)
- Repo layer for all domains: offline reads from Dexie, writes
  optimistically to Dexie and enqueue mutations for later replay
- Mutation queue with UUID idempotency keys (X-Idempotency-Key),
  FIFO flush, temp-ID reconciliation on 2xx, fail-and-continue on 4xx
- Trip sync manager: caches all trips with end_date >= today or null,
  auto-evicts 7d after end_date, fetches bundle endpoint in one request
- Map tile prefetcher: bbox from place coords, zooms 10-16, 50MB cap,
  warms SW cache via fetch
- Sync triggers: network online → flush + syncAll; WS reconnect →
  flush only (rate-limiter safe); visibilitychange/30s → flush only
- WS remoteEventHandler writes through to Dexie on every event
- Server idempotency middleware + idempotency_keys table (migration 100,
  24h TTL nightly cleanup)
- GET /api/trips/:id/bundle endpoint for efficient single-request sync
- OfflineBanner component: amber (offline) / blue (syncing) / hidden
- OfflineTab in Settings: cached trip list, re-sync and clear actions
- usePendingMutations hook for per-item pending indicators

Closes #505 #541

client/src/store/slices/placesSlice.ts

@@ -1,4 +1,4 @@
-import { placesApi } from '../../api/client'
+import { placeRepo } from '../../repo/placeRepo'
 import type { StoreApi } from 'zustand'
 import type { TripStoreState } from '../tripStore'
 import type { Place, Assignment } from '../../types'
@@ -17,7 +17,7 @@ export interface PlacesSlice {
 export const createPlacesSlice = (set: SetState, get: GetState): PlacesSlice => ({
   refreshPlaces: async (tripId) => {
     try {
-      const data = await placesApi.list(tripId)
+      const data = await placeRepo.list(tripId)
       set({ places: data.places })
     } catch (err: unknown) {
       console.error('Failed to refresh places:', err)
@@ -26,7 +26,7 @@ export const createPlacesSlice = (set: SetState, get: GetState): PlacesSlice =>
 
   addPlace: async (tripId, placeData) => {
     try {
-      const data = await placesApi.create(tripId, placeData)
+      const data = await placeRepo.create(tripId, placeData as Record<string, unknown>)
       set(state => ({ places: [data.place, ...state.places] }))
       return data.place
     } catch (err: unknown) {
@@ -36,7 +36,7 @@ export const createPlacesSlice = (set: SetState, get: GetState): PlacesSlice =>
 
   updatePlace: async (tripId, placeId, placeData) => {
     try {
-      const data = await placesApi.update(tripId, placeId, placeData)
+      const data = await placeRepo.update(tripId, placeId, placeData as Record<string, unknown>)
       set(state => {
         const updatedAssignments = { ...state.assignments }
         let changed = false
@@ -61,7 +61,7 @@ export const createPlacesSlice = (set: SetState, get: GetState): PlacesSlice =>
 
   deletePlace: async (tripId, placeId) => {
     try {
-      await placesApi.delete(tripId, placeId)
+      await placeRepo.delete(tripId, placeId)
       set(state => {
         const updatedAssignments = { ...state.assignments }
         let changed = false