Update backend-for-frontend.mdx

Broken link to API Routes in Pages Router

Author: geraldochristiano

docs/01-app/02-guides/backend-for-frontend.mdx

@@ -28,7 +28,7 @@ To implement this pattern, use:
 
 - [Route Handlers](/docs/app/api-reference/file-conventions/route)
 - [`middleware`](/docs/app/api-reference/file-conventions/middleware)
-- In Pages Router, [API Routes](/pages/building-your-application/routing/api-routes)
+- In Pages Router, [API Routes](/docs/pages/building-your-application/routing/api-routes)
 
 ## Public Endpoints