Yale-New Haven’s long-stalled $430 million proposed cancer center will now race ahead to a ground-breaking within six months and a union election among the hospital’s blue-collar workers could take place nine months later, thanks to an agreement announced by Mayor John DeStefano (at right) and hospital chief Marna Bortstrom (left) at a jubilant City Hall ceremony Wednesday evening.Labor, hospital, and political activists crammed the second-floor City Hall atrium for a hug- and whoop-filled press conference announcing a deal that culminated an almost around-the-clock, two-day negotiating bender.