Changes

docs(skills): add Jenkins PR replay testing skill (#4278)

## What
- add new skill: `test-jenkins-pipeline-changes-in-pr-by-replaying`
- document replay workflow for Jenkins pipeline changes in PRs
- include default scope rule: auto-detect PR diff unless user specifies
explicit replay scope

## Notes
- skill includes task-style PR comment tracking and retry policy
guidance

## Validation
- manual file structure/frontmatter check

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Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
 (commit: 002798f)