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/manifest.ts

@@ -0,0 +1,46 @@
+import type { MetadataRoute } from "next";
+
+export default function manifest(): MetadataRoute.Manifest {
+  return {
+    name: "میزی — پنل مدیریت کافه",
+    short_name: "میزی",
+    description: "سیستم مدیریت کافه و رستوران میزی",
+    start_url: "/fa/pos",
+    display: "standalone",
+    background_color: "#ffffff",
+    theme_color: "#0F6E56",
+    orientation: "any",
+    categories: ["business", "productivity"],
+    lang: "fa",
+    dir: "rtl",
+    icons: [
+      {
+        src: "/icons/icon-192.png",
+        sizes: "192x192",
+        type: "image/png",
+        purpose: "any",
+      },
+      {
+        src: "/icons/icon-512.png",
+        sizes: "512x512",
+        type: "image/png",
+        purpose: "any",
+      },
+      {
+        src: "/icons/icon-maskable-512.png",
+        sizes: "512x512",
+        type: "image/png",
+        purpose: "maskable",
+      },
+    ],
+    screenshots: [
+      {
+        src: "/screenshots/pos.png",
+        sizes: "1280x800",
+        type: "image/png",
+        form_factor: "wide",
+        label: "سیستم فروش حضوری",
+      },
+    ],
+  };
+}