docs: add AGENTS.md with Cursor Cloud environment notes

[maiconfz]

Summary

Adds an AGENTS.md capturing non-obvious Cursor Cloud VM setup caveats for this
repo. Standard commands remain in README.md; this file only records
environment gotchas.

Key notes captured:

• Node/npm come from nvm + Corepack (Node 24.18.0, npm@12.0.1).
• Gotcha: /exec-daemon/node (Node 22) precedes nvm on PATH; prepend the
  pinned Node bin before running scripts.
• Build + run: npm run build then node dist/bin/agents-repo.js --help.
  Subcommands (init/install/search/list) are intentional
  "not implemented yet" stubs today.

Related Issues

No tracking issue: this is a Cursor Cloud environment-setup task performed by a
Cloud agent. No public tracking issue was opened; gh is read-only in this
environment.

Workflow Checklist

• A tracking issue was opened before implementation. (N/A — Cloud
  environment setup; documented above.)
• The branch name follows the Cloud agent policy (cursor/<slug>-d971).
• This pull request was created as a draft.
• Merge to main is for human maintainers only; agents must not merge.

Change Type

• Task or chore

Scope

• Root config files (adds AGENTS.md)

Validation Checklist

• npm run env:check
• npm run lint:all
• npm run typecheck
• npm run test (build + node:test 12 + vitest 73 passed)
• npm run check:secrets

Validation Evidence

• Commands run: env:check, build, typecheck, lint:all, test,
  check:secrets.
• Key outputs: env check OK (node 24.18.0, npm 12.0.1); build OK; 73 vitest +
  12 node tests pass; node dist/bin/agents-repo.js --help and --version run.

Risk and Rollback

• Risk level: low (adds a single Markdown file; no code change).
• Rollback plan: revert the commit / delete AGENTS.md.