A coronavirus outbreak in in southern China has clogged ports critical to global trade, causing a shipping backlog that could take months to clear and lead to shortages during the year-end holiday shopping season.  The chaos began unfolding last month when authorities in the southern Chinese province of Guangdong — home to some of the world's busiest container ports — canceled flights, locked down communities and suspended trade along its coastline to bring a rapid spike in Covid-19 cases under control.  The rate of infections has since improved, and many operations have restarted ...