Add native Keito GitHub Action

[sionsmith]

Summary

• scaffold a Node 24 TypeScript GitHub Action for Keito time tracking
• implement labels, commands, activity, and auto modes against Keito API v2
• add docs, examples, CI, tests, and bundled dist/index.js

Verification

• npm run typecheck
• npm test
• npm audit
• npm run check-dist
• bundled dry-run smoke test with issues.closed fixture

Notes

• account ID resolves from account-id, account_id, or workspace_id for compatibility with keito-skill .keito/config.yml
• API keys remain input-only and are masked immediately

[sionsmith]

Marketplace readiness update:

• Removed .github/workflows/ci.yml from this action repository because GitHub Marketplace requires action repositories to contain no workflow files.
• Confirmed the repo now has a single root action.yml.
• Added README/CONTRIBUTING Marketplace release notes with the release flow and suggested categories.
• Re-ran npm run typecheck && npm test && npm run check-dist successfully.