“I decided, finally, to get a tattoo,” sings Courtney Love in her stage debut as Athena in Todd Almond’s experimental opera Kansas City Choir Boy. “It’s gonna be a bruise.” Her voice, ravaged as ever, is not what one generally hears in musicals, let alone “opera.” But it remains a powerful, visceral instrument, and when it harmonizes with Almond’s on the word “bruise,” the effect is magnificent. The one-act opened last night in New York City as part of Prototype, a critically-admired, forward-looking annual festival of small-scaled opera and musical theater works.