By Stephanie Apstein Celebrations of Team USA’s best result in the event were subdued after the Americans learned of the news following a routine screening on Sunday. BEIJING — Karen Chen had less than an hour to celebrate her dream before she returned to the nightmare. Shortly before the U.S. sealed a silver medal in the team figure skating event on Monday, her teammates learned that Vincent Zhou, who had placed third in the men’s free skate a day earlier, had tested positive for COVID-19. But Chen was due to perform in the women’s free skate, so no one told her. She finished fourth, locking …