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/sync/swConfig.ts

@@ -0,0 +1,80 @@
+/**
+ * SW cache configuration — shared between the service worker and the main thread.
+ * Uses a dedicated 'trek-sw-config' IndexedDB database (separate from trek-offline)
+ * so the SW can read it without needing to know the full trek-offline schema versions.
+ */
+import Dexie, { type Table } from 'dexie';
+
+export interface SwCacheConfig {
+  apiTtlDays: number;
+  apiMaxEntries: number;
+  tilesTtlDays: number;
+  tilesMaxEntries: number;
+}
+
+export const DEFAULT_SW_CONFIG: SwCacheConfig = {
+  apiTtlDays: 7,
+  apiMaxEntries: 500,
+  tilesTtlDays: 30,
+  tilesMaxEntries: 1000,
+};
+
+export const SW_CONFIG_BOUNDS = {
+  ttlMin: 1,
+  ttlMax: 365,
+  entriesMin: 10,
+  entriesMax: 5000,
+};
+
+export function validateSwConfig(raw: Partial<SwCacheConfig>): SwCacheConfig {
+  const clamp = (v: unknown, min: number, max: number, def: number): number => {
+    const n = Number(v);
+    return Number.isFinite(n) && n > 0 ? Math.max(min, Math.min(max, Math.round(n))) : def;
+  };
+  return {
+    apiTtlDays:     clamp(raw.apiTtlDays,     SW_CONFIG_BOUNDS.ttlMin, SW_CONFIG_BOUNDS.ttlMax, DEFAULT_SW_CONFIG.apiTtlDays),
+    apiMaxEntries:  clamp(raw.apiMaxEntries,   SW_CONFIG_BOUNDS.entriesMin, SW_CONFIG_BOUNDS.entriesMax, DEFAULT_SW_CONFIG.apiMaxEntries),
+    tilesTtlDays:   clamp(raw.tilesTtlDays,   SW_CONFIG_BOUNDS.ttlMin, SW_CONFIG_BOUNDS.ttlMax, DEFAULT_SW_CONFIG.tilesTtlDays),
+    tilesMaxEntries:clamp(raw.tilesMaxEntries, SW_CONFIG_BOUNDS.entriesMin, SW_CONFIG_BOUNDS.entriesMax, DEFAULT_SW_CONFIG.tilesMaxEntries),
+  };
+}
+
+// ── Dedicated IDB for SW config ───────────────────────────────────────────────
+
+interface SwConfigRow extends SwCacheConfig {
+  id: 'singleton';
+  updatedAt: number;
+}
+
+class SwConfigDb extends Dexie {
+  config!: Table<SwConfigRow, 'singleton'>;
+  constructor() {
+    super('trek-sw-config');
+    this.version(1).stores({ config: 'id' });
+  }
+}
+
+let _db: SwConfigDb | null = null;
+
+function getDb(): SwConfigDb {
+  if (!_db) _db = new SwConfigDb();
+  return _db;
+}
+
+export async function readSwConfigFromIDB(): Promise<SwCacheConfig | null> {
+  try {
+    const row = await getDb().config.get('singleton');
+    return row ? validateSwConfig(row) : null;
+  } catch {
+    return null;
+  }
+}
+
+export async function saveSwConfig(cfg: SwCacheConfig): Promise<void> {
+  const validated = validateSwConfig(cfg);
+  await getDb().config.put({ id: 'singleton', ...validated, updatedAt: Date.now() });
+}
+
+export async function loadSwConfig(): Promise<SwCacheConfig> {
+  return (await readSwConfigFromIDB()) ?? { ...DEFAULT_SW_CONFIG };
+}