[skill] Add mz-pr-review skill for local PR review

[mtabebe]

Add a Claude skill that runs a local code review against Materialize standards. To do so it: diffs against a base branch, then checks the change against tests (including Rust unit tests), code style, errors, architecture, and polish.

Findings are reported as Blocking / Strong suggestions / Nits.

The checklist aligns with doc/developer/guide-changes.md and guide-testing.md.

To test: run /mz-pr-review

[github-actions]

Thanks for opening this PR! Here are a few tips to help make the review process smooth for everyone.

PR title guidelines

• Use imperative mood: "Fix X" not "Fixed X" or "Fixes X"
• Be specific: "Fix panic in catalog sync when controller restarts" not "Fix bug" or "Update catalog code"
• Prefix with area if helpful: compute: , storage: , adapter: , sql:

Pre-merge checklist

• The PR title is descriptive and will make sense in the git log.
• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).

[antiguru]

Another option is to use gh diff PR, which doesn't require interacting with git.

[mtabebe]

Cool I'll add something about this. I'll fix up

[aljoscha]

I use jujutsu, not git, for determining the diff and things, but this should work for everyone

[mtabebe]

I use jujutsu, not git, for determining the diff and things, but this should work for everyone

Makes sense. IMO we should merge without jj support and then you can fix up with alternative instructions.