FREETOWN, Sierra Leone — Sierra Leone’s president declared a nationwide curfew Sunday after gunmen attacked the military’s main and largest barracks in the West African nation’s capital and then overran detention centers, including a major prison. The attack raised fears of a breakdown of order amid a surge of coups in the region. Advertisement The detention centers, including the Pademba Road Prisons — holding more than 2, 000 inmates — were attacked just as security forces fought to restore ca