docs: Adds llms.txt to docs (#47)

Author: mbleigh

third_party/docsite/src/pages/llms.txt.ts

@@ -0,0 +1,26 @@
+/**
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { getEntries } from "astro:content";
+import type { APIRoute } from "astro";
+
+export const GET: APIRoute = async ({ params, request }) => {
+  const docs = await getEntries([
+    { collection: "docs", slug: "reference" },
+    { collection: "docs", slug: "reference/frontmatter" },
+    { collection: "docs", slug: "reference/picoschema" },
+    { collection: "docs", slug: "reference/template" },
+    { collection: "docs", slug: "reference/model" },
+  ]);
+
+  return new Response(
+    `=== Dotprompt Template Format Documentation ===\n\nThe following is a complete reference to authoring files using the Dotprompt executable template format. This reference contains only information about the Dotprompt text format, not surrounding language or framework implementations.\n\n${docs
+      .map((doc) => {
+        return `# ${doc.data.title} (/${doc.slug})\n\n${doc.body}`;
+      })
+      .join("")}`,
+    { headers: { "Content-Type": "text/plain; charset=utf-8" } },
+  );
+};