NEW YORK (AP) — In his book on reinventing opera, director Yuval Sharon describes “Tristan und Isolde” as “the single hardest work in the traditional repertoire to stage.” Yet here he is, about to make his Metropolitan Opera debut at the helm of a new production of Richard Wagner’s epic love story. “It’s something I wrote before I got the job, and it’s part of why I took the job,” said Sharon, author of 2024’s “A New Philosophy of Opera.” “Because I knew it was the hardest, and I love