Stream progress for a background research task

Stream real-time progress for a background research task using Server-Sent Events (SSE). The stream starts with a connected event, followed by periodic ping comments to keep the connection alive, and closes when the task reaches a terminal status (completed, failed, or cancelled), at which point a terminal event matching the status name is sent. To replay events after reconnecting, pass ?from_id=N with the last event ID you received. After the stream closes, call GET /v1/research/{task_id} to retrieve the full result object.