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/schemas/merchant.py

@@ -90,6 +90,7 @@ class MerchantResponse(BaseModel):
 
     # Owner information
     owner_user_id: int
+    owner_email: str | None = Field(None, description="Owner's email address")
 
     # Contact Information
     contact_email: str
@@ -108,6 +109,9 @@ class MerchantResponse(BaseModel):
     created_at: str
     updated_at: str
 
+    # Store statistics
+    store_count: int = Field(0, description="Number of stores under this merchant")
+
 
 class MerchantDetailResponse(MerchantResponse):
     """
@@ -117,11 +121,9 @@ class MerchantDetailResponse(MerchantResponse):
     """
 
     # Owner details (from related User)
-    owner_email: str | None = Field(None, description="Owner's email address")
     owner_username: str | None = Field(None, description="Owner's username")
 
     # Store statistics
-    store_count: int = Field(0, description="Number of stores under this merchant")
     active_store_count: int = Field(
         0, description="Number of active stores under this merchant"
     )