58b98ab5ed
Adds nullable storage fields + availability column on tracks, remote source/source_id identity on albums/artists, TrackRepository.materialize() and get_or_create_remote() repos — groundwork for on-demand YTM library (placeholders saved without audio, materialized in-place on first play). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>