- Create _libraries.sql with libraries table (name, path, created_at) - Add library_id FK column and index to audio_files.sql - Update playlist_tracks.sql with nullable audio_file_id, SET NULL FK, and 6 phantom columns - Add af.library_id to track_metadata VIEW - Regenerate sqlc code for updated schemas - Fix playlist.go to use sql.NullInt64 for nullable audio_file_id