NEW YORK — An agreement that paves the way for the completion of the Sept. 11 museum at ground zero was reached on the eve of the 11th anniversary of the terror attacks. The memorandum of understanding between the Port Authority of New York and New Jersey and the foundation that controls the National September 11 Memorial & Museum was announced Monday. The museum was supposed to open this month, but construction all but ceased a year ago because of a funding squabble between the foundation and the Port Authority, which owns the World Trade Center site. Three powerful political …