Add CI workflow and unit tests

[LessUp]

Summary

• add a GitHub Actions workflow that installs dependencies and runs the Jest suite on pushes and pull requests
• expose core adaptive and onboarding helpers for Node environments and cover them with Jest unit tests
• document the test setup so contributors can run npm test

Testing

• npm test (fails: Jest is unavailable because dependencies could not be installed in the execution environment)

---

Codex Task