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_admin_service.py

@@ -1,14 +1,15 @@
 # tests/unit/services/test_admin_service.py
 import pytest
 
-from app.exceptions import (AdminOperationException, CannotModifySelfException,
-                            UserNotFoundException, UserStatusChangeException,
-                            VendorNotFoundException,
-                            VendorVerificationException)
+from app.exceptions import (
+    AdminOperationException,
+    CannotModifySelfException,
+    UserNotFoundException,
+    UserStatusChangeException,
+    VendorNotFoundException,
+)
 from app.services.admin_service import AdminService
 from app.services.stats_service import stats_service
-from models.database.marketplace_import_job import MarketplaceImportJob
-from models.database.vendor import Vendor
 
 
 @pytest.mark.unit