add backtest report UI to the Track Record tab

New BacktestPanel: shows qualified hit-rate/expectancy vs the all-setups baseline,
a by-direction breakdown, and the probability calibration table (predicted vs
realized, over-confident buckets flagged amber). Includes a "Run backtest" button
that triggers the job and a plain explanation of the method and its limits.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/signals/TrackRecordPanel.tsx

@@ -11,6 +11,7 @@ import { Section } from '../ui/Section';
 import { SkeletonCard } from '../ui/Skeleton';
 import { useToast } from '../ui/Toast';
 import { RECOMMENDATION_ACTION_LABELS } from '../../lib/recommendation';
+import { BacktestPanel } from './BacktestPanel';
 import type { OutcomeBucketStats } from '../../lib/types';
 
 function fmtR(value: number | null): string {
@@ -239,6 +240,9 @@ export function TrackRecordPanel() {
           </Section>
         </>
       )}
+
+      <div className="border-t border-white/[0.06] pt-2" />
+      <BacktestPanel />
     </div>
   );
 }