add dashboard layout and routing

dashboard/src/components/layout/Layout.tsx

@@ -0,0 +1,17 @@
+import { Outlet } from 'react-router-dom';
+import { Header } from './Header';
+import { Sidebar } from './Sidebar';
+
+export function Layout() {
+  return (
+    <div className="min-h-screen bg-gray-50">
+      <Header />
+      <div className="flex">
+        <Sidebar />
+        <main className="flex-1 p-6">
+          <Outlet />
+        </main>
+      </div>
+    </div>
+  );
+}