Hundreds of thousands more people were confined to their homes in northern China Tuesday as the country battled its worst COVID surge in 21 months and locked-down residents took to social media to complain about food shortages. China — where the virus emerged two years ago — has followed a “zero-COVID” strategy of tight border restrictions, lengthy quarantines, and targeted lockdowns as Beijing prepares to welcome thousands of overseas visitors to February’s Winter Olympics. But authorities have faced a resurgent virus in recent weeks, reporting 209 infections on Tuesday — the highest single-d…