Add PR review helper commands under `gh pr`

[rowan-stein]

Add PR review helper commands under gh pr

Add new commands to work with Pull Request reviews:

Commands

• gh pr see-comments — list inline review comments by review id or latest
• gh pr reply-comment — reply to a review thread comment by comment id
• gh pr review pending open — open a pending review (GraphQL)
• gh pr review pending add — add inline review comment(s) (GraphQL)
• gh pr review pending submit — submit the pending review (GraphQL)

Notes

• Use REST for list/reply operations; use GraphQL for pending review flow.
• Provide robust error handling and minimal JSON outputs; follow gh CLI conventions.

Acceptance Criteria

• Commands available under gh pr with documented flags and examples.
• Unit tests passing for new command packages.
• Basic manual smoke verified with a temporary PR.

[rowan-stein]

Upstream tracking

• Upstream issue: Add PR review helper commands under gh pr for inline comments and review flows (AI agent use cases) cli/cli#12232
• Upstream PR: Add PR review helper commands under gh pr (inline comments and review flows) cli/cli#12233

We’ll keep this issue updated as the upstream discussion progresses.