Finalize GTL and retire S/R research harness

frontend/src/lib/types.ts

@@ -399,6 +399,9 @@ export interface BacktestReport {
     horizon_days: number;
     min_lookback: number;
     cost_per_side_pct?: number;
+    target_model?: 'production_gtl' | 'structural_sr';
+    target_model_label?: string;
+    is_production_target_model?: boolean;
   };
   overall_qualified: BacktestBucket;
   overall_all: BacktestBucket;