Mayor Thomas M. Menino’s $2.5 billion municipal budget for fiscal 2013 was unanimously approved Wednesday by Boston’s City Council. The budget includes an annual cost-of-living adjustment for most pensioners, as well as $239 million for health insurance premiums for retirees and city employees. The budget is a 3 percent increase from 2012, according to the mayor’s office. The council also passed a five-year, $1.8 billion Capital Plan that includes $215 million for new project authorizations, such as infrastructure upgrades and park and community center investments.