fix(website): robots.txt also advertises the proxied docs sitemap

agenta.ai/docs/* proxies the docs site via legacy zone routing, and the old
zone-level robots override existed mainly to advertise the docs sitemap.
Listing it here means removing that override loses nothing.

Claude-Session: https://claude.ai/code/session_013Qe1Vf2yvj33BVd5W1q7HB

Author: mmabrouk

website/src/pages/robots.txt.ts

@@ -11,7 +11,7 @@ export const GET: APIRoute = () => {
 
   const body = noindex
     ? "User-agent: *\nDisallow: /"
-    : "# Agenta marketing site (https://agenta.ai)\n# Allow all crawlers full access; point them at the generated sitemap index.\nUser-agent: *\nAllow: /\n\nSitemap: https://agenta.ai/sitemap-index.xml\n";
+    : "# Agenta marketing site (https://agenta.ai)\n# Allow all crawlers full access; point them at the generated sitemap index.\n# The docs sitemap is listed too because agenta.ai/docs/* proxies the docs site.\nUser-agent: *\nAllow: /\n\nSitemap: https://agenta.ai/sitemap-index.xml\nSitemap: https://agenta.ai/docs/sitemap.xml\n";
 
   return new Response(body, {
     headers: { "Content-Type": "text/plain; charset=utf-8" },