Remove Turbopack from production build config

Turbopack cannot resolve lightningcss native .node binaries at build time.
Reverting to webpack for production builds (Turbopack dev server still works
via next dev --turbopack flag).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

next.config.ts

@@ -2,9 +2,6 @@ import type { NextConfig } from "next";
 
 const nextConfig: NextConfig = {
   output: "standalone",
-  turbopack: {
-    root: process.cwd(),
-  },
 };
 
 export default nextConfig;