Server-Sent Events stream of the caller's own notifications

Opens a long-lived text/event-stream carrying notification.created / notification.updated events (each {"unseen": <n>}), plus a : ping comment every 30s to keep the connection warm. No board access check - this is the caller's own per-user stream, the same one a board tab also subscribes to alongside its board events (see GET /projects/{id}/events). Use it on pages with no board open (settings, projects list, the notification bell) instead of opening a board subscription just to keep the bell live.