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/components/signals/BacktestPanel.tsx

@@ -285,6 +285,8 @@ export function BacktestPanel() {
                         <th className="px-4 py-2.5 text-right">Avg R</th>
                         <th className="px-4 py-2.5 text-right">Net Avg R</th>
                         <th className="px-4 py-2.5 text-right">Total R</th>
+                        <th className="px-4 py-2.5 text-right">Hold Net Avg R</th>
+                        <th className="px-4 py-2.5 text-right">Hold Total R</th>
                       </tr>
                     </thead>
                     <tbody>
@@ -303,6 +305,12 @@ export function BacktestPanel() {
                             {fmtR(row.net_avg_r ?? null)}
                           </td>
                           <td className={`num px-4 py-2.5 text-right ${rColor(row.total_r)}`}>{fmtR(row.total_r)}</td>
+                          <td className={`num px-4 py-2.5 text-right font-semibold ${rColor(row.hold_net_avg_r ?? null)}`}>
+                            {fmtR(row.hold_net_avg_r ?? null)}
+                          </td>
+                          <td className={`num px-4 py-2.5 text-right ${rColor(row.hold_total_r ?? null)}`}>
+                            {fmtR(row.hold_total_r ?? null)}
+                          </td>
                         </tr>
                       ))}
                     </tbody>