(Credit: Jeremy KNight) “Prospero’s Island,” a brand-new opera from Allen Shearer and Claudia Stevens, opened Saturday night at San Francisco’s Herbst Theater. Original, thought-provoking, engaging musical richness and full of ideas, “Prospero’s Island” was greeted by great applause. A co-production of InTandem and Ninth Planet, it was the tenth chamber opera Shearer and Stevens have composed and produced together. As {…}