By Steve Keating, Karolos Grohmann and Gabrielle Tétrault-Farber BEIJING (Reuters) – The world’s top anti-doping authority will investigate the entourage of 15-year-old Russian figure skater Kamila Valieva who tested positive for a banned drug, plunging her into a doping scandal at the Beijing Winter Olympics. Valieva, whose Olympic future will be decided after a Court of Arbitration for Sport (CAS) hearing that started at 8:30 p.m. Beijing time (1230 GMT), effortlessly completed a clean run-through of her short programme in practice on Sunday. Watching from the sidelines were her three coache…