- Rename 'Format' button to 'Quality' in settings (audio_quality/video_quality)
- Add DefaultAudioContainer and DefaultVideoContainer to UserPreferences
- Container settings now has Audio/Video sub-pickers (mp3/m4a/opus vs mp4/mkv/webm)
- Add migration 003 for new container columns
- Update repo layer and playlist flow for new fields
- Update back routing: back_quality, back_container
