AGENTS.md listed `./meteor test-packages` but not the headless
alternative. That command starts a web server and waits for a browser,
producing no terminal output, which causes LLM agents to hang.
Add `./packages/test-in-console/run.sh` alongside the existing
test-packages command in AGENTS.md with a note explaining the
difference. Also add package name examples and the PUPPETEER_DOWNLOAD_PATH
hint to the testing skill.
This commit:
- Introduces `jest` to the dev dependencies.
- Updates AGENTS.md and DEVELOPMENT.md with details about test layers and new commands.
- Adds a `jest.config.js` file targeting specific test directories.
- Splits existing test commands into `npm run test:unit` for unit tests and `npm run test:e2e` for E2E tests.
