SÃO PAULO, BRAZIL — The state government in this country’s richest and most populous city wants to move its headquarters. It plans to construct more than a dozen buildings and radically transform the city’s historic center to centralize 22,000 city workers, who are currently spread across about 60 buildings. In June, Governor Tarcísio de Freitas announced an architectural competition to design the buildings as well as monuments that he said would revitalize the city. But for the government to move, 51-year-old cook Raquel de Barros — along with her mother, husband and two teenage children — must move first. De Barros’ home is a three-story shack adjacent to the column of an abandoned industrial mill silo that gave the neighborhood its name: the Moinho slum.