Stefano Vizioli directs one of two Spoleto Festival USA operas this season, Veremonda, l’amazzone di Aragona (Veremonda, the Amazon of Aragon). In Francesco Cavalli’s opera, a royal siege is tangled with passion and comedy. Stefano talks with Jeanette Guinn about mounting an opera in the Dock Street Theatre for its American premiere and first performance in more than three centuries.