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/inventory_service.py

@@ -1,24 +1,27 @@
 # app/services/inventory_service.py
 import logging
-from datetime import datetime, timezone
-from typing import List, Optional
+from datetime import UTC, datetime
 
 from sqlalchemy.orm import Session
 
-from app.exceptions import (InsufficientInventoryException,
-                            InvalidInventoryOperationException,
-                            InvalidQuantityException,
-                            InventoryNotFoundException,
-                            InventoryValidationException,
-                            NegativeInventoryException,
-                            ProductNotFoundException, ValidationException)
+from app.exceptions import (
+    InsufficientInventoryException,
+    InvalidQuantityException,
+    InventoryNotFoundException,
+    InventoryValidationException,
+    ProductNotFoundException,
+    ValidationException,
+)
 from models.database.inventory import Inventory
 from models.database.product import Product
-from models.database.vendor import Vendor
-from models.schema.inventory import (InventoryAdjust, InventoryCreate,
-                                     InventoryLocationResponse,
-                                     InventoryReserve, InventoryUpdate,
-                                     ProductInventorySummary)
+from models.schema.inventory import (
+    InventoryAdjust,
+    InventoryCreate,
+    InventoryLocationResponse,
+    InventoryReserve,
+    InventoryUpdate,
+    ProductInventorySummary,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -58,7 +61,7 @@ class InventoryService:
             if existing:
                 old_qty = existing.quantity
                 existing.quantity = inventory_data.quantity
-                existing.updated_at = datetime.now(timezone.utc)
+                existing.updated_at = datetime.now(UTC)
                 db.commit()
                 db.refresh(existing)
 
@@ -67,24 +70,23 @@ class InventoryService:
                     f"{old_qty} → {inventory_data.quantity}"
                 )
                 return existing
-            else:
-                # Create new inventory entry
-                new_inventory = Inventory(
-                    product_id=inventory_data.product_id,
-                    vendor_id=vendor_id,
-                    location=location,
-                    quantity=inventory_data.quantity,
-                    gtin=product.marketplace_product.gtin,  # Optional reference
-                )
-                db.add(new_inventory)
-                db.commit()
-                db.refresh(new_inventory)
+            # Create new inventory entry
+            new_inventory = Inventory(
+                product_id=inventory_data.product_id,
+                vendor_id=vendor_id,
+                location=location,
+                quantity=inventory_data.quantity,
+                gtin=product.marketplace_product.gtin,  # Optional reference
+            )
+            db.add(new_inventory)
+            db.commit()
+            db.refresh(new_inventory)
 
-                logger.info(
-                    f"Created inventory for product {inventory_data.product_id} at {location}: "
-                    f"{inventory_data.quantity}"
-                )
-                return new_inventory
+            logger.info(
+                f"Created inventory for product {inventory_data.product_id} at {location}: "
+                f"{inventory_data.quantity}"
+            )
+            return new_inventory
 
         except (
             ProductNotFoundException,
@@ -162,7 +164,7 @@ class InventoryService:
                 )
 
             existing.quantity = new_qty
-            existing.updated_at = datetime.now(timezone.utc)
+            existing.updated_at = datetime.now(UTC)
             db.commit()
             db.refresh(existing)
 
@@ -224,7 +226,7 @@ class InventoryService:
 
             # Reserve inventory
             inventory.reserved_quantity += reserve_data.quantity
-            inventory.updated_at = datetime.now(timezone.utc)
+            inventory.updated_at = datetime.now(UTC)
             db.commit()
             db.refresh(inventory)
 
@@ -284,7 +286,7 @@ class InventoryService:
             else:
                 inventory.reserved_quantity -= reserve_data.quantity
 
-            inventory.updated_at = datetime.now(timezone.utc)
+            inventory.updated_at = datetime.now(UTC)
             db.commit()
             db.refresh(inventory)
 
@@ -350,7 +352,7 @@ class InventoryService:
             inventory.reserved_quantity = max(
                 0, inventory.reserved_quantity - reserve_data.quantity
             )
-            inventory.updated_at = datetime.now(timezone.utc)
+            inventory.updated_at = datetime.now(UTC)
             db.commit()
             db.refresh(inventory)
 
@@ -443,9 +445,9 @@ class InventoryService:
         vendor_id: int,
         skip: int = 0,
         limit: int = 100,
-        location: Optional[str] = None,
-        low_stock_threshold: Optional[int] = None,
-    ) -> List[Inventory]:
+        location: str | None = None,
+        low_stock_threshold: int | None = None,
+    ) -> list[Inventory]:
         """
         Get all inventory for a vendor with filtering.
 
@@ -504,7 +506,7 @@ class InventoryService:
             if inventory_update.location:
                 inventory.location = self._validate_location(inventory_update.location)
 
-            inventory.updated_at = datetime.now(timezone.utc)
+            inventory.updated_at = datetime.now(UTC)
             db.commit()
             db.refresh(inventory)
 
@@ -565,7 +567,7 @@ class InventoryService:
 
     def _get_inventory_entry(
         self, db: Session, product_id: int, location: str
-    ) -> Optional[Inventory]:
+    ) -> Inventory | None:
         """Get inventory entry by product and location."""
         return (
             db.query(Inventory)