refactor: modernize code quality tooling with Ruff

- Replace black, isort, and flake8 with Ruff (all-in-one linter and formatter)
- Add comprehensive pyproject.toml configuration
- Simplify Makefile code quality targets
- Configure exclusions for venv/.venv in pyproject.toml
- Auto-fix 1,359 linting issues across codebase

Benefits:
- Much faster builds (Ruff is written in Rust)
- Single tool replaces multiple tools
- More comprehensive rule set (UP, B, C4, SIM, PIE, RET, Q)
- All configuration centralized in pyproject.toml
- Better import sorting and formatting consistency

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/api/v1/shop/cart.py

@@ -14,9 +14,13 @@ from sqlalchemy.orm import Session
 
 from app.core.database import get_db
 from app.services.cart_service import cart_service
-from models.schema.cart import (AddToCartRequest, CartOperationResponse,
-                                CartResponse, ClearCartResponse,
-                                UpdateCartItemRequest)
+from models.schema.cart import (
+    AddToCartRequest,
+    CartOperationResponse,
+    CartResponse,
+    ClearCartResponse,
+    UpdateCartItemRequest,
+)
 
 router = APIRouter()
 logger = logging.getLogger(__name__)