Features:
- Dual-AVPlayer Smart DJ crossfade with LUFS normalization
- Mitsuha-style FFT visualizer (real-time + offline pre-computed)
- Companion API integration (Smart DJ, tag editing, vis frames)
- Offline-first SyncEngine with delta sync and album detail pre-caching
- Audio pre-fetcher for gapless queue playback
- Optimistic action queue (star/unstar with background retry)
- ShazamKit recognition with MusicKit preview playback
- Radio streaming with HLS/PLS/M3U support and buffer seek
- Watch app with Crown Sequencer and Ultra speaker support
- Batch metadata editing with album_artist fix for split albums
- Cache-first UI pattern across all views
- NWPathMonitor offline detection with reactive song greying
