feat(docs): auto-generate llms.txt via vitepress-plugin-llms

Replace static llms.txt and llms-full.txt with auto-generated versions
that stay in sync with docs on every build. The plugin also generates
per-page .md files for individual page fetching by LLMs.

apps/docs/package.json

@@ -9,7 +9,8 @@
   },
   "devDependencies": {
     "tsx": "^4.19.0",
-    "vitepress": "^1.1.4"
+    "vitepress": "^1.1.4",
+    "vitepress-plugin-llms": "^1.12.0"
   },
   "license": "AGPL-3.0"
 }