add dashboard layout and routing

dashboard/src/App.tsx

@@ -0,0 +1,33 @@
+import { BrowserRouter, Routes, Route } from 'react-router-dom';
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
+import { Layout } from './components/layout/Layout';
+import { ReviewsPage } from './pages/ReviewsPage';
+import { ReviewDetailPage } from './pages/ReviewDetailPage';
+import { MetricsPage } from './pages/MetricsPage';
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 30 * 1000,
+      retry: 1,
+    },
+  },
+});
+
+function App() {
+  return (
+    <QueryClientProvider client={queryClient}>
+      <BrowserRouter>
+        <Routes>
+          <Route path="/" element={<Layout />}>
+            <Route index element={<ReviewsPage />} />
+            <Route path="reviews/:id" element={<ReviewDetailPage />} />
+            <Route path="metrics" element={<MetricsPage />} />
+          </Route>
+        </Routes>
+      </BrowserRouter>
+    </QueryClientProvider>
+  );
+}
+
+export default App;