By Stephan Salisbury From The Philadelphia Inquirer Harry Potter, as they say in showbiz, has got legs. Next year is the 25th anniversary of the publication of the first book in the seven-book phenomenon, a coming-of-sage franchise which is now estimated to be worth in excess of $25 billion. More than 500 million copies of the J.K. Rowling novels have been sold, eight movies have been made, a theme park has been built, and stage plays have been mounted. And now, a full-blown exhibition will have its world premiere at the Franklin Institute early next year, officials announced Thursday. “Harry Potter: The Exhibition,” presented by Warner Bros. Themed Entertainment, Imagine Exhibitions, and EMC Presents, will later head off from Philadelphia to Latin America, the Asia-Pacific region, Europe, the Middle East, and Africa, the presenters said. Exact dates have not been set yet. “This exhibition will be unlike any other,” said …