Add llms.txt

[fireboy1919]

Description

Adds a statically generated /llms.txt endpoint for GraphQL.org.

• Follows the llms.txt navigation format with canonical absolute URLs
• Reuses the existing Learn page metadata so all Learn pages stay in sync
• Includes curated specification, implementation, resource, governance, community, and optional links
• Prerenders the route during the normal Next.js/Vercel build without a crawler or additional dependency
• Adds tests for the response, Learn page coverage, and canonical routes

Testing

• corepack pnpm exec node --import=tsx --test src/app/llms.txt/route.test.tsx
• corepack pnpm exec eslint --ignore-path .gitignore src/app/llms.txt
• corepack pnpm exec prettier --check src/app/llms.txt/route.ts src/app/llms.txt/render-llms-txt.ts src/app/llms.txt/route.test.tsx
• corepack pnpm exec tsc --noEmit
• corepack pnpm build (confirmed /llms.txt is prerendered as static content)

[vercel]

Someone is attempting to deploy a commit to the The GraphQL Foundation Team on Vercel.

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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: fireboy1919 / name: Rusty Phillips (3e4a85e)

[fireboy1919]

This seemed like the most natural way to do this with the existing site design since someone is already organizing the learning section.