(Photo: © Wiener Staatsoper / Michael Pöhn) The Wiener Staatsoper’s “Il Trittico” (seen June 21) was a frustrating experience due to the disparity between the excellent singers and the mediocrity of the staging. “Il Trittico” is one of Puccini’s best works both musically and dramatically. Tatjana Gürbaca’s production does not present Puccini’s three one-act operas as a sampler of contrasting {…}