feat(theme_editor): Add page for theme editor

frontend/app/[locale]/(admin)/admin/testing/page.tsx

@@ -0,0 +1,19 @@
+import { CONFIG } from "@/config/config";
+
+export default function Page() {
+  return (
+    <div className="flex h-screen bg-card">
+      <div className="flex-1 flex items-center justify-center">
+        <iframe
+          title="YouTube video player"
+          className="w-3/4 h-3/4 border bg-background rounded-md"
+          src={CONFIG.frontend_url}
+        />
+      </div>
+
+      <div className="w-96 flex-shrink-0 shadow-lg border-l p-5">
+        Theme Editor
+      </div>
+    </div>
+  );
+}