As the sirens wailed outside the ruins of Mandalay’s Sky Villa condominium and Myanmar began a minute’s silence for its more than 2,000 earthquake dead, Shwe Sin thought of her missing child.The Sky Villa block was one of Mandalay’s better housing options, with a generator offering 24-hour electricity — a rarity in war-ravaged Myanmar even before Friday’s quake — as well as a gym and a swimming pool.