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/suggestion_snoozes.sql.go

@@ -85,7 +85,7 @@ type SnoozeSuggestionParams struct {
 	Column4       float64
 }
 
-// Time-boxed "not right now" on a Discover artist suggestion (#2374).
+// Time-boxed "not right now" on a Discover artist suggestion.
 //
 // See 0049_suggestion_snoozes.up.sql for why this is a snooze and not a
 // dismissal: it records no verdict on the music, expires on its own, and