Heavy is the head that wears the crown. Timothée Chalamet’s Paul Atreides may be firmly ensconced as the Padishah Emperor, but as thrilling new footage from “ Dune: Part Three ” that Warner Bros. and Legendary released at CinemaCon on Tuesday makes clear, ruling the galaxy comes at great cost. Particularly if that means you can’t run off into the sunset with the woman you actually love, Chani (Zendaya), and instead have to be trapped in a marriage of political necessity to Florence Pugh’s