Khatia Buniatishvili is the real deal, a pianist who is fleet of fingers, yet with a relaxed, musical touch. If you’re near the Napa Valley Opera House this Saturday, and you’re planning to miss her, you might want to give that decision a rethink, especially with great seats at midrange prices available. For those of you who are excited about the fact that the Opera House is now bringing classical music to your doorstep, this is the concert of the season. Buniatishvili is doing Chopin, at which she is pretty great, and some ambitious transcriptions of orchestral pieces: Ravel’s La Valse, Stravinsky’s Petrouchka. This is not going to be one of those off-the-rack, one-size-fits-all recitals.