Two queue features:
- prev walks back through actual play history (50-entry stack), so
random modes navigate predictably instead of falling back to the
meaningless currentIndex-1 array walk.
- addNext inserts at currentIndex+1, exposed via new /play-next-song
endpoint, !playnext command, and a third "下一首播放" button on
SongCard. Insert path keeps playedIndices and history index refs
valid by shifting entries > currentIndex.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
