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/queries/lifecycle.sql

@@ -1,4 +1,4 @@
--- The download lifecycle (M502 #5523): the intervention ledger, giving a
+-- The download lifecycle: the intervention ledger, giving a
 -- download up, and seeding after import.
 
 -- name: RaiseIntervention :one
@@ -79,7 +79,7 @@ RETURNING *;
 
 -- name: CountGoneGrabs :one
 -- How many of a release's grabs ended gone since a time: a release that keeps
--- leaving its client is held back rather than taken on every pass (#6176).
+-- leaving its client is held back rather than taken on every pass.
 SELECT count(*) FROM grabs
  WHERE info_hash = sqlc.arg(info_hash) AND end_reason = 'gone' AND ended_at > sqlc.arg(since);