Debi Greenberg has finally fled the chain retailers on Newbury Street. In April, she moved her homegrown department store to an uncluttered stretch of Fort Point Channel — and while she was at it, she cropped “Boston” from the title. She says the changes reflect her decade-long pondering of an evolving American luxury consumer. Over the years, Greenberg has stocked fewer stodgy status labels and more creative, hard-to-find items by U.S. designers. But the culmination of her thinking is represented by Louis’s new building: a space that’s laid-back yet lovely, with harbor views that upstage the merchandise.