Maintainer Kit v0.2.0

Adds JSON output mode for maintainer automation.

Changes:

• Added --json support for issue, pr, release, doctor, and onboard commands
• Added JSON output test coverage
• Added GitHub Actions usage documentation
• Updated README and changelog

Maintainer Kit v0.1.0

First working release of Maintainer Kit.

Includes:

• Issue triage summaries
• Pull request review checklist
• Release notes draft command
• Repository health doctor
• Contributor onboarding guide
• Examples, tests, and GitHub community files