fix: redirector for tina ui

Author: benjamsf

src/pages/admin/index.tsx

@@ -0,0 +1,11 @@
+import React, { useEffect } from 'react';
+import useBaseUrl from '@docusaurus/useBaseUrl';
+
+export default function AdminRedirect() {
+  useEffect(() => {
+    window.location.replace(
+      useBaseUrl('/admin/index.html')
+    );
+  }, []);
+  return <p>Redirecting to Tina Admin…</p>;
+}