Only one wedding theme would do for Cassie and Lewis Byrom — the self-confessed Potterheads spent a year planning the ultimate Harry Potter wedding. It’s been a running theme throughout their romance. Lewis, 34, surprised Cassie, 31, with a letter accepting her into The Hogwarts School of Witchcraft and Wizardry for her 30th birthday, and inside the envelope were two tickets to the Harry Potter theme park in Orlando, Florida. While they were there last year, Lewis got down on one knee…