Add root page.tsx to enable middleware for homepage

Co-authored-by: huangyiirene <7665279+huangyiirene@users.noreply.github.com>

Author: Copilot

packages/site/app/page.tsx

@@ -0,0 +1,11 @@
+import { redirect } from 'next/navigation';
+
+/**
+ * Root page - redirects are handled by proxy.ts middleware
+ * This page should never actually render as the middleware intercepts and redirects
+ * But Next.js requires a page component for the route to be recognized
+ */
+export default function RootPage() {
+  // Fallback redirect if middleware didn't handle it
+  redirect('/en/docs');
+}