JAMES POMFRET and MARTIN QUIN POLLARD WHEN Yang, a Shanghai office worker, saw video clips of a burning building in western China, a disaster in which 10 people were killed, she said she could not contain her anger over tough COVID-19 measures three years into the pandemic. Watching a World Cup soccer match in a Shanghai bar two days later with her boyfriend, she spotted calls on WeChat, China's ubiquitous messaging app, for a public gathering to mourn the victims. She rushed over by bicycle to attend. "Things reached a tipping point, we had to come out," Yang, 32, who declined to…