feat(dashboard): Next.js 16 merchant panel with offline POS and PWA

Complete merchant dashboard upgrade:

Next.js 16 compatibility:
- Fix params/searchParams typed as Promise<{}> throughout App Router
- Replace middleware.ts with proxy.ts (Next.js 16 convention)
- Remove unused @ts-expect-error directives caught by stricter TS
- Cast dynamic next-intl t() keys to fix TranslateArgs type errors

Offline POS:
- IndexedDB queue (meezi_pos_offline) for orders created while offline
- Zustand sync store tracking queueCount, isSyncing, isOnline
- useOfflineSync hook: auto-syncs on reconnect/visibility-change
- SyncStatusIndicator chip in topbar (amber=offline, blue=syncing)
- submitOrderToApi falls back to local order on network failure
- Local orders skip payment flow; sync on reconnect

PWA (installable):
- @ducanh2912/next-pwa with Workbox runtime caching rules
- Web App Manifest (manifest.ts) — RTL/Farsi, theme #0F6E56
- PWA icons: 192px, 512px, maskable 512px
- next.config.ts replaces next.config.mjs

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web/dashboard/src/lib/offline/offline-db.ts

@@ -0,0 +1,111 @@
+/**
+ * IndexedDB wrapper for the POS offline order queue.
+ * All reads/writes happen in a single "order_queue" object store.
+ */
+
+export type OfflineQueueItem = {
+  /** Local UUID – primary key */
+  id: string;
+  /** "create_order" or "add_items_to_order" */
+  type: "create_order" | "add_items";
+  cafeId: string;
+  /**
+   * For add_items: the real server order ID.
+   * For create_order: null (no server ID yet).
+   */
+  targetOrderId: string | null;
+  /** Raw body to POST/PUT */
+  payload: unknown;
+  createdAt: string;
+  retries: number;
+  status: "pending" | "failed";
+};
+
+const DB_NAME = "meezi_pos_offline";
+const DB_VERSION = 1;
+const STORE = "order_queue";
+
+let _db: IDBDatabase | null = null;
+
+function openDb(): Promise<IDBDatabase> {
+  if (_db) return Promise.resolve(_db);
+  return new Promise((resolve, reject) => {
+    const req = indexedDB.open(DB_NAME, DB_VERSION);
+    req.onupgradeneeded = (e) => {
+      const db = (e.target as IDBOpenDBRequest).result;
+      if (!db.objectStoreNames.contains(STORE)) {
+        db.createObjectStore(STORE, { keyPath: "id" });
+      }
+    };
+    req.onsuccess = () => {
+      _db = req.result;
+      resolve(_db);
+    };
+    req.onerror = () => reject(req.error);
+  });
+}
+
+export async function enqueueOfflineItem(
+  item: Omit<OfflineQueueItem, "retries" | "status">
+): Promise<void> {
+  const db = await openDb();
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(STORE, "readwrite");
+    tx.objectStore(STORE).put({ ...item, retries: 0, status: "pending" });
+    tx.oncomplete = () => resolve();
+    tx.onerror = () => reject(tx.error);
+  });
+}
+
+export async function getQueueCount(): Promise<number> {
+  try {
+    const db = await openDb();
+    return new Promise((resolve, reject) => {
+      const tx = db.transaction(STORE, "readonly");
+      const req = tx.objectStore(STORE).count();
+      req.onsuccess = () => resolve(req.result);
+      req.onerror = () => reject(req.error);
+    });
+  } catch {
+    return 0;
+  }
+}
+
+export async function getAllQueueItems(): Promise<OfflineQueueItem[]> {
+  try {
+    const db = await openDb();
+    return new Promise((resolve, reject) => {
+      const tx = db.transaction(STORE, "readonly");
+      const req = tx.objectStore(STORE).getAll();
+      req.onsuccess = () => resolve(req.result as OfflineQueueItem[]);
+      req.onerror = () => reject(req.error);
+    });
+  } catch {
+    return [];
+  }
+}
+
+export async function removeQueueItem(id: string): Promise<void> {
+  const db = await openDb();
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(STORE, "readwrite");
+    tx.objectStore(STORE).delete(id);
+    tx.oncomplete = () => resolve();
+    tx.onerror = () => reject(tx.error);
+  });
+}
+
+export async function markQueueItemFailed(id: string): Promise<void> {
+  const db = await openDb();
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(STORE, "readwrite");
+    const store = tx.objectStore(STORE);
+    const getReq = store.get(id);
+    getReq.onsuccess = () => {
+      const item = getReq.result as OfflineQueueItem;
+      if (item) store.put({ ...item, status: "failed", retries: item.retries + 1 });
+    };
+    tx.oncomplete = () => resolve();
+    tx.onerror = () => reject(tx.error);
+  });
+}