fix(subscription): plan comparison + checkout read the live plan catalog

The merchant plan page hard-coded 4 tiers, prices and a feature matrix
that drifted from the admin-editable platform catalog (Starter tier
missing, stale prices/features). PlanComparison and CheckoutScreen now
consume /platform/plans + new /platform/features-catalog:

- columns = active plans by SortOrder (incl. Starter), names from
  DisplayNameFa/En, prices from MonthlyPriceToman
- limit rows from PlanLimitsData (int.MaxValue → "نامحدود")
- feature rows from the feature catalog, ticked via FeatureKeys
- checkout validates the ?plan= param against isBillableOnline and
  prices from the catalog — no more client-side price constants

fa/en/ar limit-row labels added.

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

web/dashboard/messages/fa.json

@@ -1403,6 +1403,17 @@
         "Business": "بیزنس",
         "Enterprise": "سازمانی"
       },
+      "limits": {
+        "maxOrdersPerDay": "سفارش در روز",
+        "maxBranches": "شعبه",
+        "maxTerminals": "ترمینال صندوق",
+        "maxTables": "میز",
+        "maxCustomers": "مشتری CRM",
+        "maxSmsPerMonth": "پیامک در ماه",
+        "maxMenuItems": "آیتم منو",
+        "maxReportHistoryDays": "تاریخچه گزارش (روز)",
+        "maxMenuAi3dPerMonth": "تصویر AI سه‌بعدی در ماه"
+      },
       "features": {
         "ordersPerDay": "سفارش در روز",
         "terminals": "ترمینال صندوق",