[agents] Refine review skill wiki-state handling (#147)

[coisa]

Related Issue

• Follow-up to Add a rigorous code-review skill and agent for ready PRs #147

Motivation / Context

The rigorous pull-request review skill was correctly treating .github/wiki as a high-signal surface, but it could still misread workflow-managed wiki pointer updates as unrelated drift. We also tripped over follow-up work trying to reuse historical branch and PR state after earlier branches had already been deleted. This follow-up teaches the agents to distinguish expected wiki automation state from genuine scope creep and to prefer a new bug issue plus fresh branch/PR when prior work is already closed.

Changes

• teach pull-request-review to verify wiki preview and wiki maintenance workflow context before flagging .github/wiki pointer movement as drift
• update the surface-priority reference with the repository-specific wiki automation nuance
• align review-guardian with the same rule
• teach github-pull-request and issue-implementer to check whether earlier PRs are already closed before reusing historical branch names
• prefer a fresh follow-up bug issue and new branch/PR when prior work already landed on a closed PR or deleted branch
• update the changelog entry to reflect both agent-skill refinements

Verification

• composer dev-tools changelog:check
• git diff --check

Documentation / Generated Output

• updated packaged review-skill guidance
• updated project-agent prompt guidance
• updated packaged pull-request workflow guidance
• updated CHANGELOG.md

Changelog

• Updated the Unreleased changelog entry for this follow-up to Add a rigorous code-review skill and agent for ready PRs #147 so it reflects both the wiki-state reviewer fix and the closed-branch follow-up guard.

Reviewer Notes

• .github/wiki remains locally modified in the workspace but is intentionally not part of this PR.

[github-actions]

🚀 Preview is available for this pull request.

• Docs: https://php-fast-forward.github.io/dev-tools/previews/pr-174/
• Coverage: https://php-fast-forward.github.io/dev-tools/previews/pr-174/coverage/
• Metrics: https://php-fast-forward.github.io/dev-tools/previews/pr-174/metrics/