Start Scope

Start scoping for a project without creating it.

This endpoint:

1. Streams an initial agent message
2. Runs the scope_project function
3. Streams the scope result

The frontend should connect to Socket.IO and join the scope session room before calling this endpoint to receive streaming updates.

Args: prompt: User's project prompt session_id: Session ID for Socket.IO room (client-generated) files: Optional file attachments user_id: Authenticated user ID

Returns: ScopeResponse with the scope data