feat: configure Next.js for standalone output

frontend/next.config.js

@@ -2,6 +2,7 @@
 const nextConfig = {
   reactStrictMode: true,
   // 他のカスタム設定をここに追加
+  output: 'standalone',
 };
 
 export default nextConfig;

next.config.js

@@ -0,0 +1,7 @@
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  reactStrictMode: true,
+  output: 'standalone',
+};
+
+module.exports = nextConfig;