A pair of new leases will soon bring Harry Potter and a Spanish clothing store back to the Magnificent Mile, both encouraging signals for a retail district that still has a lot of empty storefronts. Warner Bros. signed a deal for 10,000 square feet on several levels at 676 N. Michigan Ave., and plans to open an interactive exhibit dedicated to Harry Potter, while Barcelona-based Mango agreed to occupy about 16,000 square feet in the neighboring 664-670 N.