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/vendor/dashboard.py

@@ -11,9 +11,7 @@ from sqlalchemy.orm import Session
 from app.api.deps import get_current_vendor_api
 from app.core.database import get_db
 from app.services.stats_service import stats_service
-from middleware.vendor_context import require_vendor_context
 from models.database.user import User
-from models.database.vendor import Vendor
 
 router = APIRouter(prefix="/dashboard")
 logger = logging.getLogger(__name__)