Titles and navigation

src/app/groups/not-found.tsx

@@ -0,0 +1,15 @@
+import { Button } from '@/components/ui/button'
+import Link from 'next/link'
+
+export default function NotFound() {
+  return (
+    <div className="flex flex-col gap-2">
+      <p>This group does not exist.</p>
+      <p>
+        <Button asChild variant="secondary">
+          <Link href="/groups">Go to recently visited groups</Link>
+        </Button>
+      </p>
+    </div>
+  )
+}