The Playback quality setting now drives streaming: getStreamUrl appends
?quality= and useAudioPlayer feeds the server-synced streamQuality, so the
backend transcodes on demand (miss → original). Adds an optimizeTrack mutation
and an Optimize action in the metadata editor to warm a track's rendition.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>