feat: platform-aware storefront routing and billing improvements

Overhaul storefront URL routing to be platform-aware:
- Dev: /platforms/{code}/storefront/{store_code}/
- Prod: subdomain.platform.lu/ (internally rewritten to /storefront/)
- Add subdomain detection in PlatformContextMiddleware
- Add /storefront/ path rewrite for prod mode (subdomain/custom domain)
- Remove all silent platform fallbacks (platform_id=1)
- Add require_platform dependency for clean endpoint validation
- Update route registration, templates, module definitions, base_url calc
- Update StoreContextMiddleware for /storefront/ path detection
- Remove /stores/ from FrontendDetector STOREFRONT_PATH_PREFIXES

Billing service improvements:
- Add store_platform_sync_service to keep store_platforms in sync
- Make tier lookups platform-aware across billing services
- Add tiers for all platforms in seed data
- Add demo subscriptions to seed

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

app/modules/loyalty/definition.py

@@ -205,7 +205,7 @@ loyalty_module = ModuleDefinition(
                         id="loyalty",
                         label_key="storefront.account.loyalty",
                         icon="gift",
-                        route="storefront/account/loyalty",
+                        route="account/loyalty",
                         order=60,
                     ),
                 ],

app/modules/loyalty/tests/integration/test_storefront_loyalty.py

@@ -23,7 +23,7 @@ class TestStorefrontLoyaltyEndpoints:
         # Without proper store context, should return 404 or error
         response = client.get("/api/v1/storefront/loyalty/program")
         # Endpoint exists but requires store context
-        assert response.status_code in [200, 404, 422, 500]
+        assert response.status_code in [200, 403, 404, 422, 500]
 
     def test_enroll_endpoint_exists(self, client):
         """Test that enrollment endpoint is registered."""
@@ -35,16 +35,16 @@ class TestStorefrontLoyaltyEndpoints:
             },
         )
         # Endpoint exists but requires store context
-        assert response.status_code in [200, 404, 422, 500]
+        assert response.status_code in [200, 403, 404, 422, 500]
 
     def test_card_endpoint_exists(self, client):
         """Test that card endpoint is registered."""
         response = client.get("/api/v1/storefront/loyalty/card")
         # Endpoint exists but requires authentication and store context
-        assert response.status_code in [401, 404, 422, 500]
+        assert response.status_code in [401, 403, 404, 422, 500]
 
     def test_transactions_endpoint_exists(self, client):
         """Test that transactions endpoint is registered."""
         response = client.get("/api/v1/storefront/loyalty/transactions")
         # Endpoint exists but requires authentication and store context
-        assert response.status_code in [401, 404, 422, 500]
+        assert response.status_code in [401, 403, 404, 422, 500]