Revert to static export output for nginx deploy pipeline

output: "standalone" (a8f4b23) produces a Node server bundle with no
server.js at the path the deploy Dockerfile expects. The deploy repo's
Dockerfile now runs nginx serving static files (d808317), which requires
a static export (out/), not a standalone server bundle.

next.config.ts

@@ -14,7 +14,7 @@ const nextConfig: NextConfig = {
   turbopack: {
     root: path.resolve(__dirname),
   },
-  output: "standalone",
+  output: "export",
   // Required by the How It Works 3D experience. React StrictMode double-invokes
   // mount/effects in dev, which tears down and re-creates the WebGL context of
   // the heavy 32MB scene mid-initialization — the context is lost ("THREE.