- Replace Type/Quality settings with single Format button -> Audio/Video sub-pickers
- Each sub-picker shows format options (bitrates for audio, resolutions for video)
- Replace DefaultQuality with DefaultAudioFormat/DefaultVideoFormat in UserPreferences
- Add DB migration 002 for new preference columns
- Update repo layer SQL queries for new schema
- Update playlist flow to use new preference fields
- Fix missing deleteaccount and delaccount_ callback routing
- Add back_format routing for format picker navigation
