feat: grade gate-ablation variants under the hold-to-horizon exit too

The ablation judged floors under the target/stop model, but the exit
sweeps point at replacing that exit with a fixed hold — under which the
R:R floor's rationale (bigger payoff at the target) may not apply. Each
ablation row now also carries hold_avg_r / hold_net_avg_r / hold_total_r
(30d hold, initial stop only), so the Phase 3 gate decision can be read
under the exit policy that would actually be used.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/lib/types.ts

@@ -280,6 +280,11 @@ export interface BacktestTimeExitRow {
 
 export interface BacktestGateAblationRow extends BacktestBucket {
   variant: string;
+  // The same variant graded under the hold-to-horizon time exit.
+  hold_days?: number;
+  hold_avg_r?: number | null;
+  hold_net_avg_r?: number | null;
+  hold_total_r?: number | null;
 }
 
 export interface BacktestSignalEvalRow {