feat: make ticker clickable on positions page — links to company detail

Ticker column now links to /companies/{id} using a ticker→company ID
lookup. Falls back to plain text if company not found.

frontend/src/pages/Positions.tsx

@@ -1,4 +1,5 @@
-import { usePositions } from '../api/hooks';
+import { Link } from '@tanstack/react-router';
+import { usePositions, useCompanies } from '../api/hooks';
 import { DataTable, type Column } from '../components/DataTable';
 import { LoadingSpinner } from '../components/ui';
 import type { Position } from '../api/hooks';
@@ -25,6 +26,36 @@ const columns: Column<Position>[] = [
 
 export function PositionsPage() {
   const { data, isLoading } = usePositions();
+  const { data: companies } = useCompanies();
+
+  // Build ticker → company ID lookup
+  const tickerToId: Record<string, string> = {};
+  for (const c of companies ?? []) {
+    tickerToId[c.ticker] = c.id;
+  }
+
+  const posColumns: Column<Position>[] = [
+    {
+      key: 'ticker',
+      header: 'Ticker',
+      render: (r) => {
+        const companyId = tickerToId[r.ticker];
+        return companyId ? (
+          <Link to="/companies/$id" params={{ id: companyId }} className="font-mono font-semibold text-brand-300 hover:underline">
+            {r.ticker}
+          </Link>
+        ) : (
+          <span className="font-mono font-semibold text-brand-300">{r.ticker}</span>
+        );
+      },
+    },
+    { key: 'quantity', header: 'Qty' },
+    { key: 'avg_entry_price', header: 'Entry', render: (r) => <span>{fmtUsd(r.avg_entry_price)}</span> },
+    { key: 'current_price', header: 'Current', render: (r) => <span>{fmtUsd(r.current_price)}</span> },
+    { key: 'unrealized_pnl', header: 'Unrealized P&L', render: (r) => <span className={pnlColor(r.unrealized_pnl)}>{fmtUsd(r.unrealized_pnl)}</span> },
+    { key: 'realized_pnl', header: 'Realized P&L', render: (r) => <span className={pnlColor(r.realized_pnl)}>{fmtUsd(r.realized_pnl)}</span> },
+    { key: 'updated_at', header: 'Updated', render: (r) => <span className="text-xs">{new Date(r.updated_at).toLocaleString()}</span> },
+  ];
 
   if (isLoading) return <LoadingSpinner />;
 
@@ -58,7 +89,7 @@ export function PositionsPage() {
       <h1 className="mb-4 text-xl font-semibold text-gray-100">Positions</h1>
       <DataTable<Position>
         data={positions}
-        columns={columns}
+        columns={posColumns}
         keyField="id"
         footerRow={footer}
       />