Anyone living within two miles of Dupont Circle couldn’t have missed the police lockdown last night. Starting shortly after 9 p.m., D.C. police cruisers took positions along Connecticut Avenue up to the intersection with Florida Avenue, eventually shutting down all traffic — pedestrian and vehicular — without giving an explanation as to why. Two helicopters loudly hovered overhead, while overly anxious police officers screamed loudly at anyone who dared cross the street (a man walking…