feat: Add llms.txt support for AI-friendly documentation

Fixes #8117

Adds llms.txt and llms-full.txt generation following https://llmstxt.org/
spec to ensure AI models can access the latest React documentation.

- llms.txt: 13KB hierarchical link index (167 pages)
- llms-full.txt: 2.7MB full embedded documentation

Generated from sidebar configs and markdown content at build time.
Integrated into build pipeline via package.json scripts.

Author: artimath

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "analyze": "ANALYZE=true next build",
     "dev": "next-remote-watch ./src/content",
-    "build": "next build && node --experimental-modules ./scripts/downloadFonts.mjs",
+    "build": "next build && node --experimental-modules ./scripts/downloadFonts.mjs && node scripts/generate-llms-txt.js",
     "lint": "next lint && eslint \"src/content/**/*.md\"",
     "lint:fix": "next lint --fix && eslint \"src/content/**/*.md\" --fix",
     "format:source": "prettier --config .prettierrc --write \"{plugins,src}/**/*.{js,ts,jsx,tsx,css}\"",
@@ -21,6 +21,7 @@
     "postinstall": "yarn --cwd eslint-local-rules install && is-ci || husky install .husky",
     "check-all": "npm-run-all prettier lint:fix tsc rss",
     "rss": "node scripts/generateRss.js",
+    "llms": "node scripts/generate-llms-txt.js",
     "deadlinks": "node scripts/deadLinkChecker.js",
     "copyright": "node scripts/copyright.js",
     "test:eslint-local-rules": "yarn --cwd eslint-local-rules test"