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/app/q/error.tsx

@@ -0,0 +1,29 @@
+"use client";
+
+export default function QrError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string };
+  reset: () => void;
+}) {
+  return (
+    <main
+      className="flex min-h-svh flex-col items-center justify-center gap-4 bg-[#f5f5f4] p-6 text-center"
+      dir="rtl"
+    >
+      <p className="text-4xl">⚠️</p>
+      <h1 className="text-lg font-semibold text-foreground">خطا در بارگذاری منو</h1>
+      <p className="max-w-sm text-sm text-muted-foreground">
+        {error.message || "صفحه منوی میز قابل نمایش نیست."}
+      </p>
+      <button
+        type="button"
+        onClick={reset}
+        className="rounded-lg bg-[#0F6E56] px-4 py-2 text-sm font-medium text-white"
+      >
+        تلاش مجدد
+      </button>
+    </main>
+  );
+}