Chicago police and transit officials on Saturday pledged additional security for the city’s trains to stem a spike in violent crime after the shooting death of a passenger overnight. A 29-year-old man, Diuntel Moon, was shot multiple times in the chest and abdomen on a Chicago Transit Authority Red Line train on 79th Street in the Chatham neighborhood about 2 a.m. Saturday, Chicago Police Superintendent David Brown said at a news conference. Moon was pronounced dead at a hospital. No suspects are in custody, Brown said …