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_config.py

@@ -1,12 +1,9 @@
 """Tests for core configuration."""
 
-import os
-from unittest.mock import patch
 
 import pytest
 
 from notebooklm_agent.core.config import Settings, get_settings
-from notebooklm_agent.core.exceptions import NotebookLMAgentError, ValidationError
 
 
 @pytest.mark.unit

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

tests/unit/test_services/test_notebook_service.py

@@ -4,8 +4,8 @@ TDD Cycle: RED → GREEN → REFACTOR
 """
 
 from datetime import datetime
-from unittest.mock import AsyncMock, MagicMock, patch
-from uuid import UUID, uuid4
+from unittest.mock import AsyncMock, MagicMock
+from uuid import uuid4
 
 import pytest