fix: resolve __dirname error by forcing Node.js runtime on all server routes

- Add serverExternalPackages for @supabase/ssr in next.config.ts
- Add export const runtime = 'nodejs' to all pages/routes using Supabase
- Replace createAdminClient to use @supabase/supabase-js directly (no SSR)
- Prevents @supabase/ssr from running in Edge runtime on Vercel

https://claude.ai/code/session_01H2aRGDaKgarPvhay2HxN6Y

next.config.ts

@@ -1,7 +1,7 @@
 import type { NextConfig } from "next";
 
 const nextConfig: NextConfig = {
-  /* config options here */
+  serverExternalPackages: ["@supabase/ssr"],
 };
 
 export default nextConfig;