fix(lint): pin ruff version, add pre-commit hook, fix all lint errors

- Pin ruff==0.8.4 in requirements-dev.txt (was >=0.8.4, CI got newer
  version with different import sorting rules)
- Add ruff to .pre-commit-config.yaml with --fix to auto-sort imports
  on commit (prevents PyCharm import reordering from reaching CI)
- Fix I001 import sorting in 6 files
- Fix F401 unused import (sqlalchemy.Numeric in subscription.py)
- Fix noqa false positive in validate_architecture.py comment

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

tests/integration/middleware/conftest.py

@@ -26,8 +26,8 @@ from main import app
 from tests.integration.middleware.middleware_test_routes import (
     admin_router,
     api_router,
-    storefront_router,
     store_router,
+    storefront_router,
 )
 from tests.integration.middleware.middleware_test_routes import (
     router as test_router,