🦴 Add viewer backbone

apps/viewer/layouts/NotFoundPage.tsx

@@ -0,0 +1,16 @@
+import React from 'react'
+
+export const NotFoundPage = () => (
+  <div
+    style={{
+      height: '100vh',
+      display: 'flex',
+      justifyContent: 'center',
+      alignItems: 'center',
+      flexDirection: 'column',
+    }}
+  >
+    <h1 style={{ fontWeight: 'bold', fontSize: '30px' }}>404</h1>
+    <h2>The bot you&apos;re looking for doesn&apos;t exist</h2>
+  </div>
+)