commentToTimelineEntry() was dropping the attachments field, and
comment-card never rendered entry.attachments. Attachments uploaded
through the CLI (not embedded in markdown) were invisible in the UI.
- Add attachments to commentToTimelineEntry() conversion
- Add AttachmentList component that renders standalone attachments
(skipping those already referenced in the markdown content)
- Render AttachmentList in both CommentRow and CommentCard