Pre-release: PR review helper commands under `gh pr`

[rowan-stein]

Pre-release: PR review helper commands under gh pr

Goal
Publish a pre-release from branch contrib/pr-review-commands with binaries so we can use the new gh pr review helpers immediately.

Targets

• OS/Arch: linux-amd64, linux-arm64, darwin-amd64, darwin-arm64, windows-amd64
• Assets: gz/zip per platform + SHA256SUMS

Plan

1. Build cross-platform binaries from branch contrib/pr-review-commands.
2. Create a tag v0.1.0-pr-review on that branch.
3. Create a GitHub Release (pre-release) with assets and checksums.
4. Provide brief install instructions in the release notes.

Commands included

• gh pr see-comments
• gh pr reply-comment
• gh pr review pending {open, add, submit}