Still known for smokestacks and football, Cleveland is turning its ship around.Photo: Craig Hatfield"Most people know Cleveland by the Browns or The Flats," says Marc Lefkowitz. From the roof of his office building, which is dotted with native wildflowers and grasses, he gestures to the downtown skyline -- marked by the iconic Mittal Steel smokestacks that gave The Flats neighborhood its name -- and toward the beloved football team's stadium along the shimmering shores of Lake Erie. That two-pronged version of the city's reputation may be wishful thinking on the part of Lefkowitz, web editor for a local green nonprofit …