J.K. Rowling, staggeringly wealthy author of the phenomenally popular “Harry Potter” novels that begat the blockbuster film franchise, has her celebrity-pedigreed yacht “Amphitrite” available for both charter and purchase. The 156-foot-long boat, formerly christened Vajoliroja and previously owned by Johnny Depp, can be chartered at a high-season rate of about $130,000 per week, plus expenses,...