fix: judge robustness under the recommended exit, not the abandoned one

The robustness warning was computed on the target-model distribution
while the same panel recommends the hold exit — internally inconsistent.
_robustness_stats (median, profit factor, ex-top-5% expectancy) is now
shared by _bucket_stats and _time_exit_bucket, the time-exit table shows
Median Net R and Ex-Top-5% per hold length, and _build_recommendation
reads the trimmed expectancy from the recommended exit's bucket (falling
back to the target model when no hold is recommended).

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

frontend/src/components/signals/BacktestPanel.tsx

@@ -414,6 +414,8 @@ export function BacktestPanel() {
                         <th className="px-4 py-2.5 text-right">Worst R</th>
                         <th className="px-4 py-2.5 text-right">Avg Hold</th>
                         <th className="px-4 py-2.5 text-right">Net R/d</th>
+                        <th className="px-4 py-2.5 text-right">Median Net R</th>
+                        <th className="px-4 py-2.5 text-right">Ex-Top-5%</th>
                       </tr>
                     </thead>
                     <tbody>
@@ -435,6 +437,8 @@ export function BacktestPanel() {
                             <td className="num px-4 py-2.5 text-right text-red-400">{fmtR(row.worst_r)}</td>
                             <td className="num px-4 py-2.5 text-right text-gray-400">{fmtDays(row.avg_hold_days)}</td>
                             <td className={`num px-4 py-2.5 text-right ${rColor(row.net_r_per_day ?? null)}`}>{fmtRPerDay(row.net_r_per_day)}</td>
+                            <td className={`num px-4 py-2.5 text-right ${rColor(row.median_net_r ?? null)}`}>{fmtR(row.median_net_r)}</td>
+                            <td className={`num px-4 py-2.5 text-right ${rColor(row.net_avg_r_ex_top5 ?? null)}`}>{fmtR(row.net_avg_r_ex_top5)}</td>
                           </tr>
                         );
                       })}

frontend/src/lib/types.ts

@@ -259,6 +259,9 @@ export interface BacktestTimeExitRow {
   worst_r?: number | null;
   avg_hold_days?: number | null;
   net_r_per_day?: number | null;
+  median_net_r?: number | null;
+  profit_factor?: number | null;
+  net_avg_r_ex_top5?: number | null;
 }
 
 export interface BacktestPortfolioPolicy {