POST /albums/youtube/{albumId} creates the album in your library and links
every song in it, provisioning each one as an external track without queueing
any download. The external id is kept on the album so saving it twice returns
a conflict instead of a duplicate, and albums can now hold external tracks,
not just the ones you uploaded.
Eight routes under /albums covering the listing, the detail, the tracklist and
the owner-only writes, wired to the same validation filter and ErrorOr mapping
the playlists use.
Admin