Authorities arrested a South Bay apartment manager this week for allegedly running a major heroin and meth operation as well as stockpiling assault weapons mere steps from an elementary school. Brett Maxwell, 51, was charged by the Santa Clara County District Attorney’s Office after investigators raided his home and found an arsenal of about 19 firearms — including three assault rifles and several “ghost guns” — as well as explosives. Police also found about $100,000 worth of meth and heroin, and its proximity to an elementary school and city playground drew heightened concern from…..