feat: loyalty feature provider, admin data fixes, storefront mobile menu

- Add LoyaltyFeatureProvider with 11 BINARY/MERCHANT features for billing
  feature gating, wired into loyalty module definition
- Fix subscription-tiers admin page showing 0 features by populating
  feature_codes from tier relationship in all admin tier endpoints
- Fix merchants admin page showing 0 stores and N/A owner by adding
  store_count and owner_email to MerchantResponse and eager-loading owner
- Add "no tiers" warning with link in subscription creation modal when
  platform has no configured tiers
- Add missing mobile menu panel to storefront base template so hamburger
  toggle actually shows navigation links

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/tenancy/services/merchant_service.py

@@ -148,7 +148,10 @@ class MerchantService:
         Returns:
             Tuple of (merchants list, total count)
         """
-        query = select(Merchant).options(joinedload(Merchant.stores))
+        query = select(Merchant).options(
+            joinedload(Merchant.stores),
+            joinedload(Merchant.owner),
+        )
 
         # Apply filters
         if search: