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/services/cart_service.py

@@ -9,20 +9,18 @@ This module provides:
 """
 
 import logging
-from datetime import datetime, timezone
-from typing import Dict, List, Optional
 
 from sqlalchemy import and_
 from sqlalchemy.orm import Session
 
-from app.exceptions import (CartItemNotFoundException, CartValidationException,
-                            InsufficientInventoryForCartException,
-                            InvalidCartQuantityException,
-                            ProductNotAvailableForCartException,
-                            ProductNotFoundException)
+from app.exceptions import (
+    CartItemNotFoundException,
+    InsufficientInventoryForCartException,
+    InvalidCartQuantityException,
+    ProductNotFoundException,
+)
 from models.database.cart import CartItem
 from models.database.product import Product
-from models.database.vendor import Vendor
 
 logger = logging.getLogger(__name__)
 
@@ -30,7 +28,7 @@ logger = logging.getLogger(__name__)
 class CartService:
     """Service for managing shopping carts."""
 
-    def get_cart(self, db: Session, vendor_id: int, session_id: str) -> Dict:
+    def get_cart(self, db: Session, vendor_id: int, session_id: str) -> dict:
         """
         Get cart contents for a session.
 
@@ -43,7 +41,7 @@ class CartService:
             Cart data with items and totals
         """
         logger.info(
-            f"[CART_SERVICE] get_cart called",
+            "[CART_SERVICE] get_cart called",
             extra={
                 "vendor_id": vendor_id,
                 "session_id": session_id,
@@ -111,7 +109,7 @@ class CartService:
         session_id: str,
         product_id: int,
         quantity: int = 1,
-    ) -> Dict:
+    ) -> dict:
         """
         Add product to cart.
 
@@ -130,7 +128,7 @@ class CartService:
             InsufficientInventoryException: If not enough inventory
         """
         logger.info(
-            f"[CART_SERVICE] add_to_cart called",
+            "[CART_SERVICE] add_to_cart called",
             extra={
                 "vendor_id": vendor_id,
                 "session_id": session_id,
@@ -154,7 +152,7 @@ class CartService:
 
         if not product:
             logger.error(
-                f"[CART_SERVICE] Product not found",
+                "[CART_SERVICE] Product not found",
                 extra={"product_id": product_id, "vendor_id": vendor_id},
             )
             raise ProductNotFoundException(product_id=product_id, vendor_id=vendor_id)
@@ -191,7 +189,7 @@ class CartService:
             # Check inventory for new total quantity
             if product.available_inventory < new_quantity:
                 logger.warning(
-                    f"[CART_SERVICE] Insufficient inventory for update",
+                    "[CART_SERVICE] Insufficient inventory for update",
                     extra={
                         "product_id": product_id,
                         "current_in_cart": existing_item.quantity,
@@ -212,7 +210,7 @@ class CartService:
             db.refresh(existing_item)
 
             logger.info(
-                f"[CART_SERVICE] Updated existing cart item",
+                "[CART_SERVICE] Updated existing cart item",
                 extra={"cart_item_id": existing_item.id, "new_quantity": new_quantity},
             )
 
@@ -221,50 +219,49 @@ class CartService:
                 "product_id": product_id,
                 "quantity": new_quantity,
             }
-        else:
-            # Check inventory for new item
-            if product.available_inventory < quantity:
-                logger.warning(
-                    f"[CART_SERVICE] Insufficient inventory",
-                    extra={
-                        "product_id": product_id,
-                        "requested": quantity,
-                        "available": product.available_inventory,
-                    },
-                )
-                raise InsufficientInventoryForCartException(
-                    product_id=product_id,
-                    product_name=product.marketplace_product.title,
-                    requested=quantity,
-                    available=product.available_inventory,
-                )
-
-            # Create new cart item
-            cart_item = CartItem(
-                vendor_id=vendor_id,
-                session_id=session_id,
-                product_id=product_id,
-                quantity=quantity,
-                price_at_add=current_price,
-            )
-            db.add(cart_item)
-            db.commit()
-            db.refresh(cart_item)
-
-            logger.info(
-                f"[CART_SERVICE] Created new cart item",
+        # Check inventory for new item
+        if product.available_inventory < quantity:
+            logger.warning(
+                "[CART_SERVICE] Insufficient inventory",
                 extra={
-                    "cart_item_id": cart_item.id,
-                    "quantity": quantity,
-                    "price": current_price,
+                    "product_id": product_id,
+                    "requested": quantity,
+                    "available": product.available_inventory,
                 },
             )
+            raise InsufficientInventoryForCartException(
+                product_id=product_id,
+                product_name=product.marketplace_product.title,
+                requested=quantity,
+                available=product.available_inventory,
+            )
 
-            return {
-                "message": "Product added to cart",
-                "product_id": product_id,
+        # Create new cart item
+        cart_item = CartItem(
+            vendor_id=vendor_id,
+            session_id=session_id,
+            product_id=product_id,
+            quantity=quantity,
+            price_at_add=current_price,
+        )
+        db.add(cart_item)
+        db.commit()
+        db.refresh(cart_item)
+
+        logger.info(
+            "[CART_SERVICE] Created new cart item",
+            extra={
+                "cart_item_id": cart_item.id,
                 "quantity": quantity,
-            }
+                "price": current_price,
+            },
+        )
+
+        return {
+            "message": "Product added to cart",
+            "product_id": product_id,
+            "quantity": quantity,
+        }
 
     def update_cart_item(
         self,
@@ -273,7 +270,7 @@ class CartService:
         session_id: str,
         product_id: int,
         quantity: int,
-    ) -> Dict:
+    ) -> dict:
         """
         Update quantity of item in cart.
 
@@ -344,7 +341,7 @@ class CartService:
         db.refresh(cart_item)
 
         logger.info(
-            f"[CART_SERVICE] Updated cart item quantity",
+            "[CART_SERVICE] Updated cart item quantity",
             extra={
                 "cart_item_id": cart_item.id,
                 "product_id": product_id,
@@ -360,7 +357,7 @@ class CartService:
 
     def remove_from_cart(
         self, db: Session, vendor_id: int, session_id: str, product_id: int
-    ) -> Dict:
+    ) -> dict:
         """
         Remove item from cart.
 
@@ -398,7 +395,7 @@ class CartService:
         db.commit()
 
         logger.info(
-            f"[CART_SERVICE] Removed item from cart",
+            "[CART_SERVICE] Removed item from cart",
             extra={
                 "cart_item_id": cart_item.id,
                 "product_id": product_id,
@@ -408,7 +405,7 @@ class CartService:
 
         return {"message": "Item removed from cart", "product_id": product_id}
 
-    def clear_cart(self, db: Session, vendor_id: int, session_id: str) -> Dict:
+    def clear_cart(self, db: Session, vendor_id: int, session_id: str) -> dict:
         """
         Clear all items from cart.
 
@@ -432,7 +429,7 @@ class CartService:
         db.commit()
 
         logger.info(
-            f"[CART_SERVICE] Cleared cart",
+            "[CART_SERVICE] Cleared cart",
             extra={
                 "session_id": session_id,
                 "vendor_id": vendor_id,