feat(frontend): add race details page with completed metrics

Implement race detail routing and UI with client-side pace calculation so completed race metrics are visible from the calendar flow.

Made-with: Cursor

frontend/src/app/router.tsx

@@ -2,6 +2,7 @@ import { createBrowserRouter } from "react-router-dom";
 import { AppLayout } from "./layouts/AppLayout";
 import { DashboardPage } from "../pages/DashboardPage";
 import { RacesPage } from "../pages/RacesPage";
+import { RaceDetailsPage } from "../pages/RaceDetailsPage";
 
 export const appRouter = createBrowserRouter([
   {
@@ -9,7 +10,8 @@ export const appRouter = createBrowserRouter([
     element: <AppLayout />,
     children: [
       { index: true, element: <DashboardPage /> },
-      { path: "races", element: <RacesPage /> }
-    ]
-  }
+      { path: "races", element: <RacesPage /> },
+      { path: "races/:raceId", element: <RaceDetailsPage /> },
+    ],
+  },
 ]);