Create / Get / List / Update / Delete with the visibility model from
the spec: private by default, owner-only mutations, public read for
non-owners. Update uses sqlc's CASE-WHEN-flag pattern for PATCH-style
partial updates without writing N variants.
Delete cleans up the cached cover file from disk best-effort. Track
operations (Append/Remove/Reorder) and the collage generator land
in subsequent tasks.
Also adds playlists + playlist_tracks to dbtest.ResetDB's truncate
list so integration tests in this package start from a clean state.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
