Add not found boundaries

Author: aurorascharff

src/app/NotFoundContent.tsx

@@ -0,0 +1,38 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use client';
+
+import {MDXComponents} from 'components/MDX/MDXComponents';
+
+const {Intro, MaxWidth, p: P, a: A} = MDXComponents;
+
+export function NotFoundContent() {
+  return (
+    <main className="min-w-0 isolate">
+      <article className="font-normal break-words text-primary dark:text-primary-dark">
+        <div className="px-5 sm:px-12">
+          <div className="max-w-7xl mx-auto">
+            <MaxWidth>
+              <Intro>
+                <P>This page doesn’t exist.</P>
+                <P>
+                  If this is a mistake{', '}
+                  <A href="https://github.com/reactjs/react.dev/issues/new">
+                    let us know
+                  </A>
+                  {', '}
+                  and we will try to fix it!
+                </P>
+              </Intro>
+            </MaxWidth>
+          </div>
+        </div>
+      </article>
+    </main>
+  );
+}

src/app/community/not-found.tsx

@@ -0,0 +1,12 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {NotFoundContent} from '../NotFoundContent';
+
+export default function NotFound() {
+  return <NotFoundContent />;
+}

src/app/learn/not-found.tsx

@@ -0,0 +1,12 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {NotFoundContent} from '../NotFoundContent';
+
+export default function NotFound() {
+  return <NotFoundContent />;
+}

src/app/reference/not-found.tsx

@@ -0,0 +1,12 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {NotFoundContent} from '../NotFoundContent';
+
+export default function NotFound() {
+  return <NotFoundContent />;
+}