Summary

Updates contributor-facing documentation for stale PR handling and project metadata.

Linked issue

Changes

• Extend the stale PR response window from 21 to 28 days.
• Clarify what happens after a PR is closed as stale and how authors should restart the work.
• Add the Agent Friendly badge to the README badge list.

Checklist

• Tests added or updated (or N/A with reason)
• Docs / types updated if public API changed (index.d.ts and index.d.cts)
• No breaking changes (or called out explicitly above)

Summary by cubic

Updates contributor policy docs to extend the stale PR window to 28 days and clarify next steps after closure. Adds an Agent Friendly badge to the README.

Description

• Summary of changes
  • Stale PR response window: 21 → 28 days in COLLABORATOR_GUIDE.md.
  • Clarified what happens after a stale close and how authors can continue.
  • Added “Agent Friendly” badge to README.
• Reasoning
  • Give contributors more time, reduce churn, and make follow-up steps explicit.
• Additional context
  • Maintainers may pick up the work or open an issue after stale closure.

Docs

Update any mirrored contributor docs in /docs/ to reflect the 28-day window and post-close process. If the docs site shows repo badges, add the Agent Friendly badge there too.

Testing

No tests added; this is a docs-only change. No tests needed.

Semantic version impact

Patch (docs-only; no API or runtime changes).

^{Written for commit e45c7ea. Summary will update on new commits. Review in cubic}