Stale review-comment hints are now detected and suppress auto-actions

What

• The comment scan loop now tracks emptyHintReadAt and computes a hintMissed flag per thread when a comment's createdAt predates the last empty-hint read by more than a buffer, firing a comment_hint_stale telemetry event with an older_by_s measurement.
• Conditions that trigger auto-actions on newly-seen review comments now also require !hintMissed, so the auto-action doesn't fire when a hint was missed.
• The artifact live-subscribe sync transport now fires an onCommentHint callback that records telemetry with fields comment_hint, comments_empty, seed_parked, seed_skipped, and sync_transport.

Why This prevents Claude Code from auto-reacting to artifact review comments based on stale or missed signals, avoiding actions taken on outdated information.