ci(pr-review): add checkout step for skill definitions access

[chambridge]

Description

Add actions/checkout@v4 before claude-code-action to enable access to .claude/commands/ skill definitions. Uses base.sha (not head.sha) for security - this ensures skill definitions come from the trusted main branch, not from potentially malicious fork PRs.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Related Issues

Fixes the "Unknown skill: review-agentready" error seen in Claude Code Review workflow runs.
https://github.com/ambient-code/agentready/actions/runs/21011220924

Changes Made

• Added checkout step to .github/workflows/pr-review-auto-fix.yml before claude-code-action runs
• Uses actions/checkout@v4 to clone the repository
• Checks out base branch (base.sha) instead of PR head for security
  • Ensures .claude/commands/ skill definitions come from trusted main branch
  • Prevents malicious fork PRs from injecting poisoned skill files
• Fixes "Unknown skill: review-agentready" error that occurred because Claude couldn't access the skill definition file without a checkout step

Testing

• Unit tests pass (pytest)
• Integration tests pass
• Manual testing performed
• No new warnings or errors

Checklist

• My code follows the project's code style
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes

[github-actions]

🎉 This PR is included in version 2.22.1 🎉

The release is available on GitHub release

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