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/coplay.sql.go

@@ -14,7 +14,7 @@ const deleteArtistCoplayEdges = `-- name: DeleteArtistCoplayEdges :exec
 DELETE FROM artist_similarity WHERE source = 'user_cooccurrence'
 `
 
-// Household co-play similarity (#1533, milestone #160 Opt 5). Minstrel is a
+// Household co-play similarity. Minstrel is a
 // single shared-library, multi-user server (no per-user library ACL), so the
 // "household" is the whole instance's user set. These queries recompute
 // artist–artist co-occurrence edges from play_events and store them in