SYDNEY — The deadly siege began in the most incongruous of ways, on a sunny Monday morning inside a cheerful cafe in the heart of Australia's largest city. It ended 16 hours later in a barrage of gunfire that left two hostages and the Iranian-born gunman dead, and a nation that has long prided itself on its peace rocked to its core. The gunman, a self-styled cleric and a refugee with a sordid criminal history, burst into the Lindt Chocolat Cafe and took 17 people hostage.