LOS ANGELES (AP) — Katy Perry, her collaborators and her record label must pay more than $2.78 million because the pop star’s 2013 hit “Dark Horse” copied a 2009 Christian rap song, a federal jury decided Thursday. It was an underdog victory for rapper Marcus Gray, a relatively obscure artist once known as Flame, whose 5-year-old lawsuit survived constant court challenges and a trial against top-flight attorneys for Perry and the five other music-industry heavyweights who wrote her song. The amount fell well short of the nearly $20 million sought by attorneys for Gray and the two co-writers of “Joyful...