Inbound support for PR review (diff-line) comments

[amondnet]

Summary

Inbound currently covers issue + PR conversation comments (issues.listCommentsForRepo), tagged comment_type: issue|pr. PR review comments (diff-line, via pulls.listReviewCommentsForRepo) are not polled. Add them and reintroduce the pr_review value to the CommentType union (it was removed in review because it was never emitted).

Deferred from #6 / PR #7.

Tasks

• Add polling loop for pulls.listReviewCommentsForRepo (per-repo or org-wide)
• Reintroduce pr_review to the CommentType union
• Emit messages with correct comment_type: pr_review and accurate chat_id / url metadata
• Deduplicate against already-seen IDs (shared cursor strategy or separate cursor)
• Add tests covering the new polling path and pr_review message shape

Acceptance Criteria

• Review diff-line comments delivered with comment_type: pr_review
• Correct chat_id and url metadata included in each message
• Tests cover the new polling path

Additional Context

Follow-up to #6 (closed) / PR #7 (merged). The pr_review type was removed during code review in #7 because it was never emitted — this issue re-adds the full end-to-end path.