The Egyptian government acknowledged that its security forces had killed 36 Islamists in its custody Sunday, as the military leaders and the country’s Islamists vowed to keep up their fight over Egypt’s future. The news of the deaths came on a day in which there appeared to be a pause in the street battles that have claimed more than 1,000 lives in recent days, most of them Islamists and their supporters gunned down by security forces. The Islamists took measures on Sunday to avoid confrontations, including canceling several protests of the military’s ouster of a democratically elected Islamist-led government. While...