California Democrats are taking further steps to advance the state’s ambitious climate-change agenda, agreeing to regulate methane emissions from landfills and dairy farms for the first time and approving $900 million in spending on environmental programs. The approval came in the final hours of the two-year legislative session Wednesday following a flurry of negotiations involving Gov. Jerry Brown, Democratic legislative leaders and the affected industries. It was approved just a week after Democrats voted to extend California’s landmark climate change law, the most aggressive in the nation, by another 10 years, solidifying the state’s reputation as an environmental leader through at least 2030. That move, pushed by Brown and environmentalists, came amid fierce opposition from oil companies and other business interests.