fix: correct billing feature-store API paths and loyalty config

Fix feature-store.js calling /store/features/available instead of
/store/billing/features/available (missing module prefix caused 404).
Also handle platform-prefixed URLs in getStoreCode().

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

app/modules/loyalty/config.py

@@ -43,7 +43,7 @@ class ModuleConfig(BaseSettings):
     # QR code settings
     qr_code_size: int = 300  # pixels
 
-    model_config = {"env_prefix": "LOYALTY_"}
+    model_config = {"env_prefix": "LOYALTY_", "env_file": ".env", "extra": "ignore"}
 
 
 # Export for auto-discovery