feat(vercel): add Link response headers for agent discovery

Author: sriramveeraghanta

vercel.json

@@ -1,5 +1,16 @@
 {
   "cleanUrls": true,
+  "headers": [
+    {
+      "source": "/(.*)",
+      "headers": [
+        {
+          "key": "Link",
+          "value": "</llms.txt>; rel=\"describedby\"; type=\"text/plain\", </api-reference/introduction>; rel=\"service-doc\"; type=\"text/html\", </sitemap.xml>; rel=\"sitemap\"; type=\"application/xml\""
+        }
+      ]
+    }
+  ],
   "redirects": [
     {
       "source": "/api-reference",