Fix Next.js standalone build for Amplify WEB_COMPUTE

- Set output to standalone in next.config.js
- Update build artifacts to use .next/standalone
- Copy static files to standalone directory
- Remove invalid serverActions config

next.config.js

@@ -1,10 +1,7 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
   reactStrictMode: true,
-  // Ensure server-side features are enabled
-  experimental: {
-    serverActions: true,
-  },
+  output: 'standalone',
 }
 
 module.exports = nextConfig