[create-next-app] Improve AGENTS.md prompt wording (#90118)
Updates the `AGENTS.md` content generated by `create-next-app` to use
clearer wording that better signals to models that their training data
may be outdated.
The prompt wording was determined by running evals continuously until we
found a prompt that is objectively unbiased and shows no signs of
regression on any tests across all models.
**Before:**
> Next.js: ALWAYS read docs before coding
> Before any Next.js work, find and read the relevant doc in
`node_modules/next/dist/docs/`. Your training data is outdated — the
docs are the source of truth.
**After:**
> This is NOT the Next.js you know
> This version has breaking changes — APIs, conventions, and file
structure may all differ from your training data. Read the relevant
guide in `node_modules/next/dist/docs/` before writing any code. Heed
deprecation notices.
