Summary

Add pkg-pr-new to the repo so that every pull request automatically publishes a preview version of the package to pkg.pr.new.

This allows contributors and reviewers to test PR changes by installing the preview package directly, without needing a full npm release.

What needs to happen

1. Add pkg-pr-new as a dev dependency
2. Create a .github/workflows/pullrequest.yml workflow with a publish-preview job that runs npx pkg-pr-new publish on every PR

Prior art

This is already used in the agents repo — see their pullrequest.yml workflow.