After weeks of closed-door talks and days of intense debate, a proposal to extend California’s signature program for regulating global-warming greenhouse gases through the end of 2030 finally faces a showdown today in both the Senate and the Assembly. Gov. Jerry Brown, who has been making a name for himself as an international climate leader, is under tremendous pressure to pass this cap-and-trade deal — brokered by his office — over objections from some on left and the right. He has been fighting hard to win support for Assembly Bill 398, telling lawmakers last week that “This is the most important vote of your life.”