docs: add a maintainer release checklist

[afurm]

Release mechanics are intentionally not front-and-center in the README, but maintainers still need a concise checklist for cutting patch releases.

Scope:

• Add a short maintainer-facing release checklist outside the main README flow.
• Cover version bump, changelog update, full validation, GitHub Release tag naming, npm package verification, and rollback notes.
• Keep public install instructions in README.md concise.

Acceptance criteria:

• A maintainer can prepare a v0.1.x release without reading workflow YAML directly.
• The README stays focused on users and contributors, not release automation internals.
• The checklist references CHANGELOG.md.