Thousands of people stampeded during a festival in the Cambodian capital, leaving at least 345 dead and hundreds injured in what the prime minister called the country's biggest tragedy since the 1970s reign of terror by the Khmer Rouge. Some in the panicky crowd -- who were celebrating the end of the rainy season on an island in a river -- tried to flee over a bridge and were crushed underfoot or fell over its sides into the water. A witness who …