SHANGHAI, Aug 15 (Reuters) - Only a few months after beginning her career as a livestream sales host in January, Zhang Jinyu, 28, a former model and blogger with a master's degree in fashion management, had clocked hundreds of hours of broadcasting time working with brands such as YSL Beauty. A day in the life of a livestreaming host like Zhang can include more than six hours of talking almost non-stop to camera, time spent on hair, make-up, and on post-broadcast debriefs. Despite the demanding schedule, Zhang is one of millions of young Chinese people, who are facing record youth...