Add production environment guards to Keystatic routes

Implemented production environment guards in Keystatic routes to prevent access to certain functions in production mode. Updated 'layout.tsx.hbs' to redirect to home if the environment is production, and modified 'keystatic-route-handler.ts' to return 404 status code if attempting to utilize route handlers while in production.

turbo/generators/templates/keystatic/layout.tsx.hbs

@@ -1,7 +1,10 @@
+import { redirect } from 'next/navigation';
 import KeystaticAdmin from '@kit/keystatic/admin';
 
 export default function Layout() {
-  return (
-    <KeystaticAdmin />
-  );
+  if (process.env.NODE_ENV === 'production') {
+    redirect('/');
+  }
+
+  return <KeystaticAdmin />;
 }