EXCLUSIVE: Castle Rock doesn't premiere on Hulu until July 25, but San Diego Comic-Con attendees will get a lot more than a sneak peek at the psychological-horror drama. The entire opening episode of the J.J. Abrams-produced series based on Stephen King's stories will be played for fans at the confab next month, I've learned. Additionally, the home of The Handmaid's Tale is planning a big Rock presence offscreen at SDCC. Abrams is working on the next Star Wars movie over…