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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>