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_vendor_service.py

@@ -1,13 +1,16 @@
 # tests/test_vendor_service.py (updated to use custom exceptions)
 import pytest
 
-from app.exceptions import (InvalidVendorDataException,
-                            MarketplaceProductNotFoundException,
-                            MaxVendorsReachedException,
-                            ProductAlreadyExistsException,
-                            UnauthorizedVendorAccessException,
-                            ValidationException, VendorAlreadyExistsException,
-                            VendorNotFoundException)
+from app.exceptions import (
+    InvalidVendorDataException,
+    MarketplaceProductNotFoundException,
+    MaxVendorsReachedException,
+    ProductAlreadyExistsException,
+    UnauthorizedVendorAccessException,
+    ValidationException,
+    VendorAlreadyExistsException,
+    VendorNotFoundException,
+)
 from app.services.vendor_service import VendorService
 from models.schema.product import ProductCreate
 from models.schema.vendor import VendorCreate