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/README.md

@@ -0,0 +1,29 @@
+# Meezi Dashboard
+
+Next.js 14 POS dashboard for Meezi (میزی).
+
+## Setup
+
+```bash
+cd web/dashboard
+npm install
+cp .env.example .env.local
+npm run dev
+```
+
+Open [http://localhost:3000/fa/login](http://localhost:3000/fa/login)
+
+Ensure the API is running at `NEXT_PUBLIC_API_URL` (default `https://localhost:7208`).
+
+## Demo login
+
+- Phone: `09121234567`
+- OTP: check API console log (`DEV OTP for ...`) when Kavenegar is not configured
+
+## Features (Sprint 4)
+
+- i18n: `fa` (default, RTL), `ar` (RTL), `en` (LTR)
+- Dashboard layout with RTL-aware sidebar
+- POS screen: menu grid + cart + order submit
+- KDS screen: live orders + SignalR + status advance
+- Placeholder pages for upcoming modules