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_marketplace_service.py

@@ -1,20 +1,21 @@
 # tests/test_marketplace_service.py
 import uuid
-from datetime import datetime
 
 import pytest
 
 from app.exceptions.base import ValidationException
 from app.exceptions.marketplace_import_job import (
-    ImportJobCannotBeCancelledException, ImportJobCannotBeDeletedException,
-    ImportJobNotFoundException, ImportJobNotOwnedException)
-from app.exceptions.vendor import (UnauthorizedVendorAccessException,
-                                   VendorNotFoundException)
-from app.services.marketplace_import_job_service import \
-    MarketplaceImportJobService
+    ImportJobCannotBeCancelledException,
+    ImportJobCannotBeDeletedException,
+    ImportJobNotFoundException,
+    ImportJobNotOwnedException,
+)
+from app.exceptions.vendor import (
+    UnauthorizedVendorAccessException,
+    VendorNotFoundException,
+)
+from app.services.marketplace_import_job_service import MarketplaceImportJobService
 from models.database.marketplace_import_job import MarketplaceImportJob
-from models.database.user import User
-from models.database.vendor import Vendor
 from models.schema.marketplace_import_job import MarketplaceImportJobRequest