DialogOperatorAssignmentDto

{
    "user_id": "550e8400-e29b-41d4-a716-446655440000",
    "assigned_at": "2026-05-07T12:00:00Z",
    "assigned_by_user_id": "550e8400-e29b-41d4-a716-446655440000",
    "user_info": {
        "first_name": "Иван",
        "last_name": "Петров",
        "avatar_url": "https://example.com/avatar.jpg"
    }
}