chore: convert submodules to standard directories for true monorepo structure

vibn-frontend/app/api/auth/[...nextauth]/route.ts

@@ -0,0 +1,6 @@
+import NextAuth from "next-auth";
+import { authOptions } from "@/lib/auth/authOptions";
+
+const handler = NextAuth(authOptions);
+
+export { handler as GET, handler as POST };