fix: remove standalone output mode incompatible with custom server

The standalone output mode in Next.js is incompatible with the custom
server.js implementation. Removing it resolves startup warnings and
ensures proper production builds with the custom server setup.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/next.config.js

@@ -1,6 +1,5 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
-  output: 'standalone',
   eslint: {
     ignoreDuringBuilds: true,
   },