DUBAI, United Arab Emirates — U.S. airstrikes targeting Yemen’s capital killed 12 people and wounded 30 others, the Houthi rebels said early Monday. The deaths mark the latest in America’s intensified campaign of strikes targeting the rebels. The U.S. military’s Central Command declined to answer questions about the strike or discuss civilian casualties from its campaign. The Houthis described the strike as hitting the Farwa neighborhood market in Sanaa’s Shuub district. That area has been