Ending a summer concert with a blinding display of fireworks is a widespread tradition, but Friday’s (August 24) grand finale of the La Jolla Music Society’s SummerFest 2012 kept all of the dramatic fireworks on the Sherwood Auditorium stage. Under the demanding baton of guest conductor Kent Nagano, the festival chamber orchestra tore into what could have been just another neat program of standard repertory and kept us alert with consistently exhilarating playing. From the breakneck tempo of Rossini’s Overture to The Barber of Seville, a felicitous program-opener, Nagano pushed his 40-member ensemble beyond their evident comfort zone. He demanded…