- Added preferences management in `preferences.py` with functions to load, save, get, set, and reset preferences.
- Introduced a configuration directory structure based on the operating system.
- Integrated preferences into the settings window, allowing users to reset settings and manage window geometry.
- Enhanced `search_filter.py` to support flexible date column names and improved filtering logic.
- Updated `settings_window.py` to include options for managing backup and configuration folder paths.
- Introduced an `UndoManager` class to handle undo actions for add/update/delete operations.
- Improved UIManager to support sorting in tree views and added a toast notification feature.
- Introduced `quick_test.py` for running specific test categories (unit, integration, theme, all).
- Updated `run_tests.py` to improve test execution and reporting, including coverage.
- Removed outdated test scripts for keyboard shortcuts, menu theming, note saving, and entry updating.
- Added new test script `test_theme_changing.py` to verify theme changing functionality.
- Consolidated integration tests into `test_integration.py` for comprehensive testing of TheChart application.
- Updated theme manager to ensure color retrieval works correctly.
- Modified test constants to import from the correct module path.
