feat: implement real-time 3D audio spatialization
- Refactor Snd3d to update gain and panning in real-time via the Ticker interface.
- Use std::atomic for gain and pan to ensure thread-safe updates between the main and audio threads.
- Fix logic errors in stereo panning calculations within Sample and Sink.
- Implement ticker cleanup in Scene to prevent leaks and crashes.
- Adjust CrystalGroupBlue light color to purple to match its visual model.
- Update project TODO list and refine the development journal entry.