Recitals by the pianist Sara Daneshpour have become a highlight of the American Art Museum’s annual Steinway Series, and her probing and often fiery performance Sunday afternoon showed why. Daneshpour’s near-impeccable technique is impressive enough, but in a program that included the musings of Robert Schumann and the eruptive violence of Sergei Prokofiev, Daneshpour also brought an intensity and seriousness of purpose that had you at the edge of your seat.