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>

tests/unit/services/test_inventory_service.py

@@ -3,17 +3,16 @@ import uuid
 
 import pytest
 
-from app.exceptions import (InsufficientInventoryException,
-                            InvalidInventoryOperationException,
-                            InvalidQuantityException,
-                            InventoryNotFoundException,
-                            InventoryValidationException,
-                            NegativeInventoryException, ValidationException)
+from app.exceptions import (
+    InsufficientInventoryException,
+    InvalidQuantityException,
+    InventoryNotFoundException,
+    InventoryValidationException,
+)
 from app.services.inventory_service import InventoryService
 from models.database.inventory import Inventory
 from models.database.marketplace_product import MarketplaceProduct
-from models.schema.inventory import (InventoryAdd, InventoryCreate,
-                                     InventoryUpdate)
+from models.schema.inventory import InventoryAdd, InventoryCreate, InventoryUpdate
 
 
 @pytest.mark.unit