feat: scaffold react dashboard

frontend/src/App.tsx

@@ -0,0 +1,8 @@
+export default function App() {
+  return (
+    <div className="app">
+      <h1>Discord Moderation Dashboard</h1>
+      <p>React/Vite scaffold - dashboard components coming soon</p>
+    </div>
+  );
+}