docs: query comments say what each query selects and why, not how it came to be (#6277)

Rewrites the internal/db/queries comments to rule 32 and regenerates
dbq, whose doc comments and embedded SQL carry them. The bugs behind the
tiered mixes, the md5 order seed, the score bands and the round-robin
arms are restated as the constraint each one enforces; counts from one
library and stale cross-references are gone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/dbq/likes.sql.go

@@ -93,7 +93,7 @@ type LikeTrackParams struct {
 	TrackID pgtype.UUID
 }
 
-// A like is on the song (M498 #5438): every copy of it sharing the track's
+// A like is on the song: every copy of it sharing the track's
 // song_key is liked. Returns the tracks newly liked, for the sync log; empty
 // when the song was already liked.
 func (q *Queries) LikeTrack(ctx context.Context, arg LikeTrackParams) ([]pgtype.UUID, error) {