Test that AGENTS.md's claims stay true against templates/

The guardrail document is dense with concrete, checkable claims about the generated project: Makefile targets (`make smoke`), directory layout (`docs/bruno/environments/Local.bru`, `docs/bruno/example/`), package paths, and the `httpx` / `auth` API surface. Nothing today stops any of those from silently becoming false when `templates/` changes — a renamed target or moved directory leaves the doc confidently instructing an agent to do something impossible, which is worse than having no guardrail at all.

The idea is a test on gonext's side that extracts the referenced targets and paths from `AGENTS.md` and asserts each one exists in the embedded `templates/` tree. Scope of what's extractable (paths and Make targets only, versus also validating Go symbols in the code samples) is open.

Came out of an ideation session around #13, not a scoped request.

Start with AGENTS.md and the embedded templates/ tree, then inspect the existing gonext tests or template-loading entry points. Decide whether the guardrail covers paths and Make targets only or also Go symbols, and make the test fail when a referenced target or path is absent from templates/.

Written by the indexing model from the issue text.