Add a 404 page to the standard open saas template (#281)

* Add a 404 page to the standard open saas template

* Revert "Add a 404 page to the standard open saas template"

This reverts commit c9e407323286aa6c0b2ba618abc4c9f63bdb3dcd.

* reinstate 404 page after mistake with patch script

template/app/main.wasp

@@ -309,6 +309,11 @@ page AdminUIButtonsPage {
   authRequired: true,
   component: import AdminUI from "@src/admin/elements/ui-elements/ButtonsPage"
 }
+
+route NotFoundRoute { path: "*", to: NotFoundPage }
+page NotFoundPage {
+  component: import { NotFoundPage } from "@src/client/components/NotFoundPage"
+}
 //#endregion
 
 //#region Contact Form Messages

template/app/src/client/components/NotFoundPage.tsx

@@ -0,0 +1,19 @@
+import React from 'react';
+import { Link } from 'react-router-dom';
+
+export function NotFoundPage() {
+  return (
+    <div className='flex items-center justify-center min-h-screen'>
+      <div className='text-center'>
+        <h1 className='text-6xl font-bold  mb-4'>404</h1>
+        <p className='text-lg text-bodydark mb-8'>Oops! The page you're looking for doesn't exist.</p>
+        <Link
+          to='/'
+          className='inline-block px-8 py-3 text-white bg-primary rounded-lg hover:bg-secondary transition duration-300'
+        >
+          Go Back Home
+        </Link>
+      </div>
+    </div>
+  );
+}