Last week’s battle of the orchestras may be eclipsed by this week’s. Besides the local symphonic ensembles, there are some visitors in the ring, too. The common theme is the piano concerti of Johannes Brahms, both of them disarmingly beautiful pieces, and here is how we call it. THE ORCHESTRAS >> The week starts strong with the Cleveland Orchestra on Monday (October 15, 8 p.m.) in the Kennedy Center Concert Hall. Washington Performing Arts Society…