Refine Character Voices waveform and discovery
Implementation details:
- Add normalized cached waveform rendering to the trim timeline
- Add bounded playback progress with a smooth playhead
- Anchor the trim transcription warning outside layout flow
- Stop node schema queries from forcing voice discovery rescans
- Deduplicate background discovery refreshes across instances
Follow-up to #318
- Add socket import for proper resource handling
- Force garbage collection on thread exit to clean up resources
- Wrap thread exit in finally block to ensure cleanup happens
- Fixes ConnectionResetError exceptions on Windows when background refresh finishes