(Credit: Cory Weaver / San Francisco Opera) Billy Budd, Foretopman, is the center of the conflict between evil and good, dark and light, vulnerable and powerful in Benjamin Britten’s masterpiece  “Billy Budd.” Picking this opera for the second night opening of San Francisco’s 97th season was a masterful choice. Everything – the music, drama, ethical conflict, suspenseful, challenging, rewarding – {…}