The combined seed_info CTE filtered the seed out when its genre was
NULL/empty. Restored the spec's two-CTE design (seed_artist + seed_tags)
so similar-artist matching works regardless of the seed's genre coverage.
Drops the genre workaround from the SimilarArtist test.
Single SELECT that joins tracks with general_likes (for is_liked) and
an aggregated LATERAL subquery on play_events (for last_played_at,
play_count, skip_count). Excludes seed + tracks played in the last
N hours. Drives the M3 weighted shuffle scoring.