SHANGHAI (Reuters) – The tensions of lockdown have exposed divisions among Shanghai residents, pitting young against old, locals against outsiders, and above all, COVID-negative against COVID-positive people. Shanghai’s 25 million people, most of whom live in apartment blocks, have forged new communal bonds during the city’s coronavirus outbreak, through barter and group buying and setting up food-sharing stations. But with no end in sight to a lockdown that for some has lasted four weeks, frustrations are also mounting behind the shuttered gates of the city’s tower blocks, often playing out w…