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/components/placeholder-page.tsx

@@ -0,0 +1,15 @@
+"use client";
+
+import { useTranslations } from "next-intl";
+
+export function PlaceholderPage({ titleKey }: { titleKey: string }) {
+  const tNav = useTranslations("nav");
+  const tCommon = useTranslations("common");
+  return (
+    <div className="flex h-64 items-center justify-center rounded-lg border border-dashed border-border">
+      <p className="text-muted-foreground">
+        {tNav(titleKey as "crm")} — {tCommon("comingSoon")}
+      </p>
+    </div>
+  );
+}