refactor: migrate to Next.js with edge functions and update relay utilities

- Removed old relay utilities and tests, replacing them with a new structure under `src/lib/relay-utils.ts`.
- Implemented a new edge function in `app/api/proxy/route.ts` to handle proxy requests.
- Created a new Next.js layout and page structure for the frontend, including a user interface for testing the proxy.
- Added Tailwind CSS for styling and configured PostCSS.
- Updated TypeScript configuration for better compatibility with Next.js.
- Removed unused files and configurations related to the previous setup.

next.config.ts

@@ -0,0 +1,7 @@
+import type { NextConfig } from 'next';
+
+const nextConfig: NextConfig = {
+  /* config options here */
+};
+
+export default nextConfig;