docs: Fix the link on the server-api page to the reference (#97)

Author: katmayb

src/langgraph-platform/server-api-ref.mdx

@@ -4,7 +4,7 @@ sidebarTitle: Server API
 ---
 The LangGraph Server API reference is available within each deployment at the `/docs` endpoint (e.g. `http://localhost:8124/docs`).
 
-Click <a href="https://langchain-ai.github.io/langgraph/cloud/reference/api/api_ref/" target="_blank">here</a> to view the API reference.
+View the [API reference](https://langchain-ai.github.io/langgraph/cloud/reference/api/api_ref.html).
 
 ## Authentication