docs: add error page (#13839)

www/apps/user-guide/app/fonts.ts

@@ -0,0 +1,12 @@
+import { Inter, Roboto_Mono } from "next/font/google"
+
+export const inter = Inter({
+  subsets: ["latin"],
+  variable: "--font-inter",
+  weight: ["400", "500"],
+})
+
+export const robotoMono = Roboto_Mono({
+  subsets: ["latin"],
+  variable: "--font-roboto-mono",
+})