@claude review — option to auto-delete previous review comments on the same PR

When using @claude review on a PR multiple times (e.g., after pushing new changes), previous review comments accumulate and clutter the PR timeline. There's no way to delete them from Graphite's UI, and GitHub's UI only shows "Edit" — not "Delete" — for these comments.

Request: Add an option (either a config flag or default behavior) to automatically delete previous @claude review comments on the same PR when posting a new review.

Why:

• Stale reviews are noise — only the latest review is relevant
• On PRs with multiple revisions, the comment thread becomes hard to follow
• Manually deleting via gh api -X DELETE works but shouldn't be necessary

Suggested behavior: When @claude review posts a new review comment, delete any prior review comments authored by the Claude bot on that same PR.