Both return user's starred artists/albums/songs sorted liked_at DESC.
Cap at 500 entries per category for v1 (Subsonic spec doesn't define
pagination on these endpoints; M3+ can revisit if needed).
Validate-all-first atomicity on star: a missing entity refuses the whole
call with Subsonic error 70. Unstar is a best-effort delete (missing
entities are no-ops, matching client expectations after library moves).
bvandeusen