feat(dashboard): simplify navigation — frequency-based IA

The sidebar had 22 items in 5 accordion groups, all defaulting closed:
first visit showed five vague headers and zero destinations, there was
no Dashboard/Home link at all, and rare pages (taxes, subscription) had
equal weight with POS. Restructured around usage frequency:

- Flat primary (always visible, no header): Dashboard, POS, Tables,
  Kitchen, Queue, Reservations, Menu, Reports
- Two collapsible groups: Customers & marketing (crm, coupons, sms,
  reviews, discover) and Café management (inventory, expenses, shifts,
  taxes, hr, branches)
- Footer utility icons: settings, subscription, support
- Removed "notifications" from the nav (duplicate of the topbar bell)

Other fixes folded in:
- Deleted [locale]/page.tsx which redirected "/" to /pos — it made the
  POS exit button a no-op loop and left OverviewScreen unreachable.
  "/" now renders the overview home; login still lands on /pos.
- Branch gating moved from group-level to an item whitelist
  (BRANCH_ALLOWED_NAV_KEYS) — also closes the hole where branch
  accounts could deep-link to /reports etc. past the RouteGuard.
- RouteGuard now checks footer items too (subscription stays gated).
- revalidate=300 on the locale layout: Next emitted s-maxage=31536000
  and the WCDN edge kept serving year-old HTML shells after deploys.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/dashboard/messages/fa.json

@@ -113,12 +113,10 @@
     "collapseSidebar": "جمع کردن نوار کناری",
     "expandSidebar": "باز کردن نوار کناری",
     "groups": {
-      "operations": "عملیات روزانه",
-      "menuSales": "منو و فروش",
-      "customers": "مشتریان",
-      "finance": "گزارش و مالی",
+      "customers": "مشتریان و بازاریابی",
       "management": "مدیریت کافه"
     },
+    "home": "داشبورد",
     "pos": "صندوق",
     "tables": "میزها",
     "crm": "مشتریان",