feat(docs): add agent skills discovery instructions to llms.txt

Replace the single-line skills registry link with structured
instructions that tell agents how to discover, fetch, and prioritize
skills. Mirrors the pattern from dfinity/developer-docs.

Author: marc0olo

docs-site/plugins/astro-agent-docs.mjs

@@ -66,6 +66,9 @@ function findSection(filePath) {
 function generateLlmsTxt(pages, siteUrl, basePath) {
   const base = (siteUrl + basePath).replace(/\/$/, "");
 
+  const skillsBase =
+    "https://skills.internetcomputer.org/.well-known/skills";
+
   // Extract version from base path (e.g., "/0.2/" → "0.2", "/main/" → "main")
   const version = basePath.replace(/^\/|\/$/g, "") || null;
   const title = version
@@ -77,7 +80,17 @@ function generateLlmsTxt(pages, siteUrl, basePath) {
     "",
     "> Command-line tool for developing and deploying applications on the Internet Computer Protocol (ICP).",
     "",
-    "Agent skills for IC development: https://skills.internetcomputer.org/.well-known/skills/index.json",
+    "## Agent skills",
+    "",
+    "Tested implementation patterns for ICP development are available as agent skills.",
+    "Before writing any ICP code, fetch the skills index and remember the skill names and descriptions:",
+    `${skillsBase}/index.json`,
+    "",
+    "When a task matches a skill description, fetch its content on-demand from:",
+    `${skillsBase}/{name}/{file}`,
+    "",
+    "Skills contain correct dependency versions, configuration formats, and common pitfalls that prevent build failures.",
+    "Always prefer skill guidance over general documentation when both cover the same topic.",
     "",
   ];