feat: ticker search, watchlist momentum column, alpha vs S&P 500

Three usability fixes:

1. Global ticker search in the sidebar (TickerSearch) — typeahead over the
   tracked universe that opens a ticker's detail page without adding it to the
   watchlist. Also wired into the mobile nav.

2. Watchlist table shows the ticker's 12-1 momentum percentile (the top-pick
   selector) instead of the noisy full S/R-level list. Enriched from the setup
   already loaded in watchlist_service._enrich_entry — no extra query.

3. Alpha vs the S&P 500 on paper trades (open + closed). New benchmark_prices
   table + benchmark_service store SPY daily closes (a standalone series, not a
   Ticker, so it never enters the scanner / momentum ranking / rankings) via a
   new daily-pipeline step. paper_trade_service computes per-trade
   benchmark_return / alpha_pct / alpha_usd over each holding period; the open-
   trades table, dashboard, and closed-trades panel surface per-trade and total
   alpha. The list read path never makes a provider call.

Deploy: alembic upgrade head, then run the benchmark/daily job once to populate
SPY closes (alpha shows "—" until then).

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

frontend/src/components/signals/MyTradesPanel.tsx

@@ -38,6 +38,7 @@ export function MyTradesPanel() {
     const rows = (closed ?? []).map((t) => ({ t, p: tradePnl(t) }));
     const rs = rows.map((r) => r.p?.r).filter((r): r is number => r != null);
     const pnls = rows.map((r) => r.p?.pnl ?? 0);
+    const alphas = rows.map((r) => r.t.alpha_usd).filter((a): a is number => a != null);
     const wins = pnls.filter((p) => p > 0).length;
     const losses = pnls.filter((p) => p < 0).length;
     const decided = wins + losses;
@@ -49,6 +50,7 @@ export function MyTradesPanel() {
       avgR: rs.length ? rs.reduce((a, b) => a + b, 0) / rs.length : null,
       totalR: rs.length ? rs.reduce((a, b) => a + b, 0) : null,
       totalPnl: pnls.reduce((a, b) => a + b, 0),
+      totalAlpha: alphas.length ? alphas.reduce((a, b) => a + b, 0) : null,
       rows,
     };
   }, [closed]);
@@ -64,11 +66,12 @@ export function MyTradesPanel() {
         </Callout>
       ) : (
         <div className="space-y-4">
-          <div className="grid gap-3 sm:grid-cols-2 lg:grid-cols-4">
+          <div className="grid gap-3 sm:grid-cols-2 lg:grid-cols-5">
             <Stat label="Hit Rate" value={stats.hitRate != null ? `${stats.hitRate.toFixed(1)}%` : '—'} sub={`${stats.wins}W / ${stats.losses}L`} />
             <Stat label="Expectancy" value={fmtR(stats.avgR)} valueClass={color(stats.avgR)} sub="avg R per closed trade" />
             <Stat label="Total R" value={fmtR(stats.totalR)} valueClass={color(stats.totalR)} sub={`${stats.total} closed`} />
             <Stat label="Total P&L" value={money(stats.totalPnl)} valueClass={color(stats.totalPnl)} sub="realized, all closed" />
+            <Stat label="Alpha vs S&P 500" value={stats.totalAlpha != null ? money(stats.totalAlpha) : '—'} valueClass={color(stats.totalAlpha)} sub="realized vs buy-and-hold SPY" />
           </div>
 
           <div className="glass overflow-x-auto">
@@ -81,6 +84,7 @@ export function MyTradesPanel() {
                   <th className="px-4 py-2.5 text-right">Exit</th>
                   <th className="px-4 py-2.5 text-right">P&L</th>
                   <th className="px-4 py-2.5 text-right">R</th>
+                  <th className="px-4 py-2.5 text-right">Alpha</th>
                   <th className="px-4 py-2.5 text-right">Closed</th>
                 </tr>
               </thead>
@@ -97,6 +101,7 @@ export function MyTradesPanel() {
                     <td className="num px-4 py-2.5 text-right text-gray-300">{t.close_price != null ? formatPrice(t.close_price) : '—'}</td>
                     <td className={`num px-4 py-2.5 text-right font-semibold ${p ? color(p.pnl) : 'text-gray-500'}`}>{p ? money(p.pnl) : '—'}</td>
                     <td className={`num px-4 py-2.5 text-right ${p?.r != null ? color(p.r) : 'text-gray-500'}`}>{p?.r != null ? fmtR(p.r) : '—'}</td>
+                    <td className={`num px-4 py-2.5 text-right ${t.alpha_pct != null ? color(t.alpha_pct) : 'text-gray-500'}`} title="Return vs. S&P 500 over the holding period">{t.alpha_pct != null ? `${t.alpha_pct >= 0 ? '+' : ''}${t.alpha_pct.toFixed(1)}%` : '—'}</td>
                     <td className="num px-4 py-2.5 text-right text-gray-500">{t.closed_at ? new Date(t.closed_at).toLocaleDateString() : '—'}</td>
                   </tr>
                 ))}