docs: Document context servers (#21170)

This PR adds documentation for context servers.

Release Notes:

- N/A

.cloudflare/docs-proxy/src/worker.js

@@ -3,15 +3,6 @@ export default {
     const url = new URL(request.url);
     url.hostname = "docs-anw.pages.dev";
 
-    // These pages were removed, but may still be served due to Cloudflare's
-    // [asset retention](https://developers.cloudflare.com/pages/configuration/serving-pages/#asset-retention).
-    if (
-      url.pathname === "/docs/assistant/context-servers" ||
-      url.pathname === "/docs/assistant/model-context-protocol"
-    ) {
-      return await fetch("https://zed.dev/404");
-    }
-
     let res = await fetch(url, request);
 
     if (res.status === 404) {