feat: show current position on company detail trends tab

Displays an 'Open Position' card above the trend charts when we hold
a position in that ticker. Shows shares, avg entry price, current
price, market value, and unrealized P&L with green/red coloring.
Card is hidden when no position exists for the ticker.

frontend/src/pages/CompanyDetail.tsx

@@ -15,6 +15,7 @@ import {
   useTrendHistory,
   useMarketPrices,
   useDocument,
+  usePositions,
 } from '../api/hooks';
 import { StatusBadge, ConfidenceBar, LoadingSpinner, Card } from '../components/ui';
 import { DataTable, type Column } from '../components/DataTable';
@@ -45,6 +46,7 @@ export function CompanyDetailPage() {
   const { data: trends } = useTrends({ ticker: company?.ticker, limit: 200 });
   const { data: trendHistory } = useTrendHistory({ ticker: company?.ticker, limit: 500 });
   const { data: marketPrices } = useMarketPrices(company?.ticker, 200);
+  const { data: positions } = usePositions(company?.ticker);
   const [tab, setTab] = useState<'trends' | 'sources' | 'aliases' | 'macro' | 'competitors' | 'patterns' | 'signals' | 'decisions'>('trends');
 
   if (isLoading || !company) return <LoadingSpinner />;
@@ -83,7 +85,10 @@ export function CompanyDetailPage() {
       </div>
 
       {tab === 'trends' && (
-        <TrendHistoryChart trends={trendHistory ?? []} latestTrends={trends ?? []} ticker={company.ticker} marketPrices={marketPrices ?? []} />
+        <div className="space-y-4">
+          <PositionCard positions={positions ?? []} ticker={company.ticker} />
+          <TrendHistoryChart trends={trendHistory ?? []} latestTrends={trends ?? []} ticker={company.ticker} marketPrices={marketPrices ?? []} />
+        </div>
       )}
 
       {tab === 'sources' && (
@@ -615,6 +620,48 @@ function TrendTooltip({ active, payload, label }: Record<string, unknown>) {
   );
 }
 
+function PositionCard({ positions, ticker }: { positions: import('../api/hooks').Position[]; ticker: string }) {
+  const pos = positions.find((p) => p.ticker === ticker && p.quantity > 0);
+  if (!pos) return null;
+
+  const marketValue = pos.current_price ? pos.quantity * pos.current_price : null;
+  const pnlColor = (pos.unrealized_pnl ?? 0) >= 0 ? 'text-green-400' : 'text-red-400';
+  const pnlSign = (pos.unrealized_pnl ?? 0) >= 0 ? '+' : '';
+
+  return (
+    <Card>
+      <div className="flex items-center justify-between">
+        <h2 className="text-sm font-medium text-gray-400">Open Position</h2>
+        <StatusBadge status="active" />
+      </div>
+      <dl className="mt-2 grid grid-cols-2 gap-x-8 gap-y-2 text-sm sm:grid-cols-5">
+        <div>
+          <dt className="text-gray-500">Shares</dt>
+          <dd className="font-mono text-gray-200">{pos.quantity}</dd>
+        </div>
+        <div>
+          <dt className="text-gray-500">Avg Entry</dt>
+          <dd className="font-mono text-gray-200">${pos.avg_entry_price.toFixed(2)}</dd>
+        </div>
+        <div>
+          <dt className="text-gray-500">Current Price</dt>
+          <dd className="font-mono text-gray-200">{pos.current_price ? `$${pos.current_price.toFixed(2)}` : '—'}</dd>
+        </div>
+        <div>
+          <dt className="text-gray-500">Market Value</dt>
+          <dd className="font-mono text-gray-200">{marketValue ? `$${marketValue.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 })}` : '—'}</dd>
+        </div>
+        <div>
+          <dt className="text-gray-500">Unrealized P&L</dt>
+          <dd className={`font-mono font-semibold ${pnlColor}`}>
+            {pos.unrealized_pnl != null ? `${pnlSign}$${Math.abs(pos.unrealized_pnl).toFixed(2)}` : '—'}
+          </dd>
+        </div>
+      </dl>
+    </Card>
+  );
+}
+
 function TrendHistoryChart({ trends, latestTrends, ticker, marketPrices }: { trends: TrendSummary[]; latestTrends: TrendSummary[]; ticker: string; marketPrices: MarketPrice[] }) {
   const [selectedWindow, setSelectedWindow] = useState('7d');