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/coverart_settings.sql.go

@@ -77,7 +77,7 @@ SELECT provider_id, enabled, api_key, display_order, created_at, updated_at
  ORDER BY display_order, provider_id
 `
 
-// M7 cover-sources: queries for the cover_art_provider_settings table
+// Queries for the cover_art_provider_settings table
 // and the cover_art_sources_meta singleton. The SettingsService
 // consumes these.
 // Returns all rows from cover_art_provider_settings. Used by the
@@ -155,7 +155,7 @@ type UpsertProviderSettingsParams struct {
 
 // INSERT a default row for a newly-registered provider, or update an
 // existing row's display_order on boot reconciliation. Does NOT
-// overwrite enabled / api_key on conflict — the operator's settings
+// overwrite enabled / api_key on conflict — an admin's settings
 // persist across restarts.
 func (q *Queries) UpsertProviderSettings(ctx context.Context, arg UpsertProviderSettingsParams) error {
 	_, err := q.db.Exec(ctx, upsertProviderSettings, arg.ProviderID, arg.Enabled, arg.DisplayOrder)