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/components/admin/ActivationSettings.tsx

@@ -4,7 +4,7 @@ import { useActivationSettings, useUpdateActivationSettings } from '../../hooks/
 import { SkeletonTable } from '../ui/Skeleton';
 
 const DEFAULTS: ActivationConfig = {
-  min_expected_value: 0.15,
+  min_momentum_percentile: 80,
   min_rr: 1.2,
   min_confidence: 55,
   min_target_probability: 0,
@@ -40,26 +40,27 @@ export function ActivationSettings() {
         <h3 className="text-sm font-semibold text-gray-200">Activation Gate</h3>
         <p className="mt-1 text-xs text-gray-500">
           What counts as a signal worth acting on. Drives the Dashboard's "Qualified" metric, the
-          Signals "Qualified only" view, and the Track Record's qualified stats. The core test is
-          <span className="text-gray-300"> expected value</span> — probability-weighted asymmetry —
-          so R:R and target probability no longer fight each other. All setups are still evaluated
-          regardless; tune the EV floor against the Track Record's EV sweep to see what actually wins.
+          Signals "Qualified only" view, and the Track Record's qualified stats. The core selection is
+          <span className="text-gray-300"> cross-sectional momentum</span> — the ticker must rank in the
+          top slice of the universe by 12-1 month momentum, the one signal the backtest showed predicts
+          forward returns. R:R and confidence stay as floors. Tune the cutoff against the Track Record's
+          momentum sweep to see what actually wins.
         </p>
       </div>
 
       <div className="grid gap-4 md:grid-cols-3">
         <label className="block space-y-1">
-          <span className="text-xs text-gray-400">Min Expected Value (R)</span>
+          <span className="text-xs text-gray-400">Min Momentum Percentile</span>
           <input
             type="number"
-            min={-1}
-            max={10}
-            step={0.05}
-            value={form.min_expected_value}
-            onChange={(e) => setForm((prev) => ({ ...prev, min_expected_value: Number(e.target.value) }))}
+            min={0}
+            max={100}
+            step={5}
+            value={form.min_momentum_percentile}
+            onChange={(e) => setForm((prev) => ({ ...prev, min_momentum_percentile: Number(e.target.value) }))}
             className="w-full input-glass px-3 py-2 text-sm"
           />
-          <span className="text-[11px] text-gray-600">p·R:R − (1−p), in R. 0.15 ≈ +0.15× risk/trade. The core gate.</span>
+          <span className="text-[11px] text-gray-600">Ticker's 12-1 momentum rank. 80 = top 20% of the universe. 0 disables. The core gate.</span>
         </label>
         <label className="block space-y-1">
           <span className="text-xs text-gray-400">Min Risk:Reward (1 : x)</span>
@@ -89,7 +90,7 @@ export function ActivationSettings() {
 
       <div className="border-t border-white/[0.06] pt-4">
         <p className="text-xs font-medium uppercase tracking-widest text-gray-500">Optional tighteners</p>
-        <p className="mt-1 text-[11px] text-gray-600">Off by default — turn on to be more selective on top of the EV gate.</p>
+        <p className="mt-1 text-[11px] text-gray-600">Off by default — turn on to be more selective on top of the momentum gate.</p>
         <div className="mt-3 grid gap-3 md:grid-cols-3">
           <label className="block space-y-1">
             <span className="text-xs text-gray-400">Min Target Probability (%)</span>