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/pages/DashboardPage.tsx

@@ -100,8 +100,10 @@ export default function DashboardPage() {
   const exposure = useMemo(() => {
     const rows = openTrades.data ?? [];
     let riskUsd = 0, unrealUsd = 0, unrealR = 0, rPriced = 0, winners = 0, losers = 0;
+    let alphaUsd = 0, alphaPriced = 0;
     for (const t of rows) {
       riskUsd += Math.abs(t.entry_price - t.stop_loss) * t.shares;
+      if (t.alpha_usd != null) { alphaUsd += t.alpha_usd; alphaPriced += 1; }
       const p = tradePnl(t);
       if (!p) continue;
       unrealUsd += p.pnl;
@@ -109,7 +111,7 @@ export default function DashboardPage() {
       if (p.pnl > 0) winners += 1;
       else if (p.pnl < 0) losers += 1;
     }
-    return { count: rows.length, riskUsd, unrealUsd, unrealR, rPriced, winners, losers };
+    return { count: rows.length, riskUsd, unrealUsd, unrealR, rPriced, winners, losers, alphaUsd, alphaPriced };
   }, [openTrades.data]);
 
   return (
@@ -141,11 +143,11 @@ export default function DashboardPage() {
 
       {/* Metric strip */}
       {(trades.isLoading || openTrades.isLoading) ? (
-        <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-4">
-          <SkeletonCard /><SkeletonCard /><SkeletonCard /><SkeletonCard />
+        <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-5">
+          <SkeletonCard /><SkeletonCard /><SkeletonCard /><SkeletonCard /><SkeletonCard />
         </div>
       ) : (
-        <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-4">
+        <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-5">
           <Metric
             label="Live Setups"
             value={String(trades.data?.length ?? 0)}
@@ -172,6 +174,16 @@ export default function DashboardPage() {
                 : 'mark-to-market'
             }
           />
+          <Metric
+            label="Alpha vs S&P 500"
+            value={exposure.alphaPriced > 0 ? money(exposure.alphaUsd) : '—'}
+            valueClass={
+              exposure.alphaPriced > 0
+                ? exposure.alphaUsd >= 0 ? 'text-emerald-400' : 'text-red-400'
+                : 'text-gray-100'
+            }
+            sub={exposure.alphaPriced > 0 ? `${exposure.alphaPriced} open · vs buy-and-hold SPY` : 'vs buy-and-hold SPY'}
+          />
         </div>
       )}