chore(lint): apply ruff --fix (4443 auto-fixes)

Auto-fixed categories:
- F401: unused imports removed
- I001: import blocks sorted
- W293: trailing whitespace stripped
- UP035: deprecated typing imports replaced
- SIM: simplify suggestions applied
- ARG: unused args prefixed with underscore
- T201: print statements removed
- F841: unused variables removed
- RUF059: unpacked variables prefixed

Remaining ~1500 unfixable errors (C901, B904, N806, E402) require manual work.

Backend smoke tests: 13/13 passed.

backend/tests/core/test_defensive_guards.py

@@ -1,15 +1,17 @@
+import shutil
 import sys
 from pathlib import Path
-import shutil
-import pytest
 from unittest.mock import MagicMock, patch
+
+import pytest
 from git.exc import InvalidGitRepositoryError
 
 sys.path.insert(0, str(Path(__file__).parent.parent.parent))
 
-from src.services.git_service import GitService
-from src.core.superset_client import SupersetClient
 from src.core.config_models import Environment
+from src.core.superset_client import SupersetClient
+from src.services.git_service import GitService
+
 
 # [DEF:test_git_service_get_repo_path_guard:Function]
 # @RELATION: BINDS_TO -> UnknownModule