refactor: replace single PR review with bulk review command

Replace review-pr command with review-pending-prs to enable efficient
batch review of open PRs. New command fetches up to 10 unreviewed PRs,
performs automated checks, and provides bulk actions (close rejected,
label approved, request fixes).

🤖 Generated with Claude Code (https://claude.ai/code)
Co-Authored-By: Claude <[email protected]>