migrate to vercel; bump version

src/pages/robots.txt.ts

@@ -0,0 +1,13 @@
+import type { APIRoute } from "astro";
+
+const getRobotsTxt = (sitemapURL: URL) => `
+User-agent: *
+Allow: /
+
+Sitemap: ${sitemapURL.href}
+`;
+
+export const GET: APIRoute = ({ site }) => {
+  const sitemapURL = new URL("sitemap-index.xml", site);
+  return new Response(getRobotsTxt(sitemapURL));
+};