Revert to standalone output: static export cannot run the SMTP Server Action

output: "export" produces pure static HTML with no server at runtime, so
the contact form's Server Action (src/actions/sendEmail.ts, nodemailer/SMTP)
can never execute under it - Next.js itself refuses to build with a Server
Action present under output: "export". The deploy architecture is being
switched to a Node standalone runtime (see doormile-build) instead, which
supports the existing Server Action unchanged.

next.config.ts

@@ -14,7 +14,7 @@ const nextConfig: NextConfig = {
   turbopack: {
     root: path.resolve(__dirname),
   },
-  output: "export",
+  output: "standalone",
   // 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.