[codex] Add GitHub Actions workflows

[Standed]

What changed

• Added a CI workflow for push to main and pull requests across Ubuntu and macOS on Node 24.
• Added a tag-based release workflow that runs tests, packs the npm package, uploads release assets, and publishes to npm when NPM_TOKEN is configured.

Why

This gives the project a repeatable GitHub validation and release path without committing local build artifacts or dependencies.

Validation

• npm test