remove output setting

Author: FunamaYukina

frontend/apps/app/next.config.ts

@@ -15,7 +15,6 @@ if (process.env.VERCEL_ENV === 'production') {
 const nextConfig: NextConfig = {
   // Server-only packages that should not be bundled on the client
   serverExternalPackages: ['@mastra/*'],
-  output: 'standalone',
 
   // NOTE: Exclude Prisma-related packages from the bundle
   // These packages are installed separately in the node_modules/@prisma directory