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/loyalty/definition.py

@@ -44,6 +44,13 @@ def _get_storefront_router():
     return storefront_router
 
 
+def _get_feature_provider():
+    """Lazy import of feature provider to avoid circular imports."""
+    from app.modules.loyalty.services.loyalty_features import loyalty_feature_provider
+
+    return loyalty_feature_provider
+
+
 # Loyalty module definition
 loyalty_module = ModuleDefinition(
     code="loyalty",
@@ -213,6 +220,8 @@ loyalty_module = ModuleDefinition(
             options={"queue": "scheduled"},
         ),
     ],
+    # Feature provider for billing feature gating
+    feature_provider=_get_feature_provider,
 )