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.

internal/store/retention_test.go

@@ -130,7 +130,7 @@ func TestRetainWithAuditCountsItsOwnRow(t *testing.T) {
 		}
 	}
 
-	res, err := s.RetainWithAudit(ctx, RetentionPolicy{ActionsLogMaxRows: 3}, "scheduler", "bodies_cleared=0")
+	res, err := s.RetainWithAudit(ctx, RetentionPolicy{ActionsLogMaxRows: 3}, "scheduler")
 	if err != nil {
 		t.Fatalf("RetainWithAudit() error = %v", err)
 	}