Add React race hub frontend

frontend/src/components/Nav.tsx

@@ -0,0 +1,16 @@
+import { Link } from '@tanstack/react-router'
+
+export function Nav() {
+  return (
+    <nav className="app-nav">
+      <Link to="/" className="nav-logo">
+        box<em>-</em>box
+      </Link>
+      <div className="nav-links">
+        <Link to="/race-hub" search={{}} activeProps={{ className: 'active' }}>
+          Race Hub
+        </Link>
+      </div>
+    </nav>
+  )
+}