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/format-datetime.ts

@@ -0,0 +1,30 @@
+import { format } from "date-fns-jalali";
+import { enUS } from "date-fns-jalali/locale/en-US";
+import { faIR } from "date-fns-jalali/locale/fa-IR";
+
+const PLAN_TIERS = ["Free", "Pro", "Business", "Enterprise"] as const;
+export type PlanTierKey = (typeof PLAN_TIERS)[number];
+
+export function isPlanTierKey(tier: string): tier is PlanTierKey {
+  return (PLAN_TIERS as readonly string[]).includes(tier);
+}
+
+export function numberLocaleForUi(locale: string): string {
+  if (locale === "en") return "en-US";
+  if (locale === "ar") return "ar-SA";
+  return "fa-IR";
+}
+
+export function formatHeaderTime(date: Date, locale: string): string {
+  return date.toLocaleTimeString(numberLocaleForUi(locale), {
+    hour: "2-digit",
+    minute: "2-digit",
+    second: "2-digit",
+    hour12: false,
+  });
+}
+
+export function formatHeaderJalaliDate(date: Date, locale: string): string {
+  const jalaliLocale = locale === "en" ? enUS : faIR;
+  return format(date, "EEEE d MMMM yyyy", { locale: jalaliLocale });
+}