Add a comment to a ticket's discussion thread. Requires the `ticket_id` (from create_ticket or list_tickets) and the `content` of the comment. The `ticket_id` may be a bare number (e.g. `123`) or the fully prefixed form (e.g. `workspace-123`); only tickets from the current workspace can be commented on. Comments are visible to the user and to all agents who later work on the ticket, making them the primary way to communicate context and decisions across the ticket's lifecycle. Note that comments are always attributed to the Manager role, regardless of which agent calls the tool.