YOKOHAMA, Japan — President Obama ended a 10-day diplomatic and economic journey through Asia on a personal note Sunday, visiting a colossal copper Buddha that he had seen as a 6-year-old boy, then headed for Washington to confront the lame-duck Congress on Monday. He told President Dmitri A. Medvedev of Russia here that his “top priority” on foreign policy for the Congressional session is ratification of their new arms control treaty, which is stalled in the Senate.