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/layout/Sidebar.tsx

@@ -3,6 +3,7 @@ import { useQuery } from '@tanstack/react-query';
 import { useAuthStore } from '../../stores/authStore';
 import { check as healthCheck } from '../../api/health';
 import { getRunningJobs } from '../../api/jobs';
+import TickerSearch from './TickerSearch';
 
 const navItems = [
   { to: '/', label: 'Overview', index: '01', end: true },
@@ -54,6 +55,10 @@ export default function Sidebar() {
         <p className="text-[10px] text-gray-500 mt-1.5 font-mono uppercase tracking-[0.22em]">Trading Intelligence</p>
       </div>
 
+      <div className="px-3 pt-4">
+        <TickerSearch />
+      </div>
+
       <nav className="flex-1 px-3 py-5 space-y-1">
         {navItems.map(({ to, label, index, end }) => (
           <NavLink key={to} to={to} end={end} className={({ isActive }) => linkClasses(isActive)}>