feat: scaffold frontend app structure

frontend/src/pages/DashboardPage.tsx

@@ -0,0 +1,8 @@
+export function DashboardPage(): JSX.Element {
+  return (
+    <section className="page page--dashboard">
+      <h1 className="page__title">Dashboard</h1>
+      <p className="page__subtitle">Overview cards and quick actions will be added in the next task.</p>
+    </section>
+  );
+}