refactor: fix linting issues and code quality

- Fix import ordering in __init__.py
- Remove unused imports from dependencies.py
- Fix import sorting across multiple files
- Apply ruff auto-fixes

No functional changes

tests/unit/test_core/test_logging.py

@@ -1,9 +1,8 @@
 """Tests for logging module."""
 
-from unittest.mock import MagicMock, patch
+from unittest.mock import patch
 
 import pytest
-import structlog
 
 from notebooklm_agent.core.config import Settings
 from notebooklm_agent.core.logging import setup_logging