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/qr-menu-texture.ts

@@ -0,0 +1,34 @@
+import type { CSSProperties } from "react";
+
+/** QR guest menu background textures (owner picks in Settings → Appearance). */
+
+export const CAFE_MENU_TEXTURES = [
+  "none",
+  "paper",
+  "linen",
+  "dots",
+  "grid",
+  "marble",
+  "wood",
+  "warm",
+] as const;
+
+export type CafeMenuTexture = (typeof CAFE_MENU_TEXTURES)[number];
+
+export function normalizeMenuTexture(value?: string | null): CafeMenuTexture {
+  if (value && (CAFE_MENU_TEXTURES as readonly string[]).includes(value)) {
+    return value as CafeMenuTexture;
+  }
+  return "none";
+}
+
+/** Props for the textured QR menu shell (uses CSS in globals.css). */
+export function qrMenuTextureShellProps(
+  texture: CafeMenuTexture,
+  backgroundColor: string
+): { "data-qr-texture": CafeMenuTexture; style: CSSProperties } {
+  return {
+    "data-qr-texture": texture,
+    style: { ["--qr-bg" as string]: backgroundColor },
+  };
+}