- Remove outdated `undo-state.md`
- Add two code quality/optimization reports that were used to guide previous work:
- `code-report.md` (optimization)
- `code-report-quality.md` (stability and code health)
- Add `themes.md`.
- Update undo system docs and roadmap.
- Add visual file picker for GUI with toggle support.
- Introduce `GUIConfig` class for loading GUI settings from configuration file.
- Refactor window initialization to support dynamic sizing based on configuration.
- Add macOS-specific handling for fullscreen behavior.
- Improve header inclusion order and minor code cleanup.