release: document npm publish process for maintainers

[shrey16]

Goal

Add maintainer-facing documentation for publishing the npm package safely.

Current state

The repo has a Publish npm package GitHub Actions workflow. It runs on GitHub Release publish or manual dry-run dispatch. It does not publish on ordinary pushes.

Acceptance

• Document version bump rules.
• Document creating a GitHub Release such as v0.2.10.
• Document that manual workflow dispatch defaults to dry-run.
• Document required NPM_TOKEN repo secret without exposing its value.
• Include the verification commands maintainers should run before release.