replace EV activation gate with cross-sectional 12-1 momentum ranking

The 5-year backtest confirmed the EV gate adds negative value (high threshold =
worst expectancy) and that 12-1 month momentum is the one price signal with a
plausible, right-signed cross-sectional IC (~0.05). So "qualified" now means:
clears the R:R + confidence floors AND the ticker ranks in the top
`min_momentum_percentile` of the universe by 12-1 momentum that week.

- qualification.py: drop expected_value_r / the EV gate; add a momentum-percentile
  gate (duck-typed `momentum_percentile`, only enforced when attached + threshold
  set, else defers to floors). Mirrored in frontend qualification.ts.
- activation config/schema: min_expected_value -> min_momentum_percentile
  (default 80 = top quintile). ActivationSettings, DashboardPage (ranks/【shows】
  momentum instead of EV), and the BacktestPanel sweep follow.
- backtest: rank each ISO week's universe by 12-1 momentum, assign a percentile,
  and qualify the top slice; the sweep now sweeps the percentile cutoff.

Also offload the backtest's per-ticker compute to a worker thread so the heavy
~5y run no longer blocks the API event loop (the "backend offline" flicker).

Production setups don't carry momentum_percentile yet — wiring the scanner to
attach it (a universe momentum-rank step) is the next step; until then the live
gate defers to floors while the backtest measures the momentum selection. 330
backend tests pass; frontend build clean.

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

frontend/src/pages/DashboardPage.tsx

@@ -12,7 +12,7 @@ import { OpenTradesPanel } from '../components/dashboard/OpenTradesPanel';
 import { SkeletonCard, SkeletonTable } from '../components/ui/Skeleton';
 import { formatPrice } from '../lib/format';
 import { recommendationActionLabel } from '../lib/recommendation';
-import { qualifiesSetup, activationSummary, primaryTargetProbability, expectedValueR } from '../lib/qualification';
+import { qualifiesSetup, activationSummary, primaryTargetProbability } from '../lib/qualification';
 import type { TradeSetup } from '../lib/types';
 
 function fmtR(value: number | null): string {
@@ -69,12 +69,12 @@ export default function DashboardPage() {
   );
 
   // Show qualified setups first; fall back to the full list when none qualify.
-  // Rank by expected value (R) so the best opportunity sits at the top.
+  // Rank by 12-1 momentum percentile so the strongest names sit at the top.
   const showingQualified = qualifiedSetups.length > 0;
   const topSetups: TradeSetup[] = useMemo(() => {
     const pool = showingQualified ? qualifiedSetups : trades.data ?? [];
     return [...pool]
-      .sort((a, b) => (expectedValueR(b) ?? -Infinity) - (expectedValueR(a) ?? -Infinity))
+      .sort((a, b) => (b.momentum_percentile ?? -Infinity) - (a.momentum_percentile ?? -Infinity))
       .slice(0, 5);
   }, [showingQualified, qualifiedSetups, trades.data]);
 
@@ -176,13 +176,12 @@ export default function DashboardPage() {
                       <th className="px-4 py-3 text-right">Entry</th>
                       <th className="px-4 py-3 text-right">R:R</th>
                       <th className="px-4 py-3 text-right">Target&nbsp;Prob</th>
-                      <th className="px-4 py-3 text-right">Exp.&nbsp;Value</th>
+                      <th className="px-4 py-3 text-right">Momentum</th>
                       <th className="hidden px-4 py-3 md:table-cell">Action</th>
                     </tr>
                   </thead>
                   <tbody>
                     {topSetups.map((setup, i) => {
-                      const ev = expectedValueR(setup);
                       const isTopPick = i === 0;
                       return (
                         <tr
@@ -212,8 +211,8 @@ export default function DashboardPage() {
                               return p != null ? `${Math.round(p)}%` : '—';
                             })()}
                           </td>
-                          <td className={`num px-4 py-3 text-right font-semibold ${rColor(ev)}`}>
-                            {fmtR(ev)}
+                          <td className="num px-4 py-3 text-right font-semibold text-gray-200">
+                            {setup.momentum_percentile != null ? `${Math.round(setup.momentum_percentile)}%ile` : '—'}
                           </td>
                           <td className="hidden px-4 py-3 text-xs text-gray-400 md:table-cell">
                             {recommendationActionLabel(setup.recommended_action)}
@@ -225,7 +224,7 @@ export default function DashboardPage() {
                 </table>
                 <div className="flex items-center justify-between border-t border-white/[0.04] px-4 py-2.5">
                   <span className="text-[11px] text-gray-500">
-                    Exp. Value = probability-weighted payoff per unit of risk
+                    Momentum = ticker's 12-1 month rank across the universe (higher = stronger)
                   </span>
                   <Link to="/signals" className="text-xs font-medium text-blue-300 hover:text-blue-200 transition-colors">
                     All setups →