LOS ANGELES — Chart-topping R&B star Rihanna is delving into the world of fashion, starring in a reality television show competition that will challenge designers to make outfits for a handful of celebrities, US cable channel Style Network said on Wednesday. “Styled to Rock,” set to premiere in the latter half of 2013, will feature 12 young designers handpicked by the Barbadian Grammy-winning singer. The singer will also serve as an executive producer under her given name, Robyn Rihanna Fenty. Style Network has yet to announce which celebrities will guest host or the fashion experts who will serve as mentors to contestants. — Reuters