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/acquisition.sql.go

@@ -147,7 +147,7 @@ type ListAcquisitionServicesRow struct {
 	UpdatedAt        pgtype.Timestamptz
 }
 
-// Indexers and download clients (M502 #5518).
+// Indexers and download clients.
 // Returns no secret, only whether one is set: this feeds the settings page.
 func (q *Queries) ListAcquisitionServices(ctx context.Context) ([]ListAcquisitionServicesRow, error) {
 	rows, err := q.db.Query(ctx, listAcquisitionServices)