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/inventory-units.ts

@@ -0,0 +1,20 @@
+/** Common warehouse units (Persian labels stored on the API). */
+export const INVENTORY_UNITS = [
+  { value: "عدد", key: "piece" },
+  { value: "گرم", key: "gram" },
+  { value: "کیلوگرم", key: "kilogram" },
+  { value: "میلی‌لیتر", key: "milliliter" },
+  { value: "لیتر", key: "liter" },
+  { value: "سی‌سی", key: "cc" },
+  { value: "بسته", key: "pack" },
+  { value: "قوطی", key: "can" },
+  { value: "کیسه", key: "bag" },
+] as const;
+
+export const INVENTORY_UNIT_VALUES = INVENTORY_UNITS.map((u) => u.value);
+
+export type InventoryUnitValue = (typeof INVENTORY_UNIT_VALUES)[number];
+
+export function isKnownInventoryUnit(unit: string): boolean {
+  return INVENTORY_UNIT_VALUES.includes(unit as InventoryUnitValue);
+}