fix(lint): auto-fix ruff violations and tune lint rules

- Auto-fixed 4,496 lint issues (import sorting, modern syntax, etc.)
- Added ignore rules for patterns intentional in this codebase:
  E402 (late imports), E712 (SQLAlchemy filters), B904 (raise from),
  SIM108/SIM105/SIM117 (readability preferences)
- Added per-file ignores for tests and scripts
- Excluded broken scripts/rename_terminology.py (has curly quotes)

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

app/modules/billing/services/billing_service.py

@@ -15,15 +15,6 @@ from datetime import datetime
 
 from sqlalchemy.orm import Session
 
-from app.modules.billing.services.stripe_service import stripe_service
-from app.modules.billing.services.subscription_service import subscription_service
-from app.modules.billing.models import (
-    AddOnProduct,
-    BillingHistory,
-    MerchantSubscription,
-    SubscriptionTier,
-    StoreAddOn,
-)
 from app.modules.billing.exceptions import (
     BillingServiceError,
     NoActiveSubscriptionError,
@@ -32,6 +23,15 @@ from app.modules.billing.exceptions import (
     SubscriptionNotCancelledError,
     TierNotFoundError,
 )
+from app.modules.billing.models import (
+    AddOnProduct,
+    BillingHistory,
+    MerchantSubscription,
+    StoreAddOn,
+    SubscriptionTier,
+)
+from app.modules.billing.services.stripe_service import stripe_service
+from app.modules.billing.services.subscription_service import subscription_service
 
 logger = logging.getLogger(__name__)