retention: compose the audit detail in the store with the real body count

RetainWithAudit now takes only the actor; the store builds the detail after
body clearing so bodies_cleared is a real number, and still writes the row
before the cap.

cmd/email-agent/main.go

@@ -346,9 +346,7 @@ func runRetain(cfg *config.Config, logger *slog.Logger) error {
 	}
 	// The audit row is written inside the same transaction, before the cap, so
 	// the cap counts it. This is what keeps actions_log bounded across runs.
-	detail := fmt.Sprintf("bodies_cleared=%%d retention_days=%d max_rows=%d",
-		cfg.RetentionDays, cfg.ActionsLogMaxRows)
-	res, err := st.RetainWithAudit(ctx, policy, "scheduler", detail)
+	res, err := st.RetainWithAudit(ctx, policy, "scheduler")
 	if err != nil {
 		return err
 	}