PORT-AU-PRINCE, Haiti—Haiti’s political future on Sunday grew murkier after the surprise return of First Lady Martine Moïse, who was released from a hospital in Miami where she was treated for injuries following an attack in which the president was assassinated. Martine Moïse did not make any public statements after she descended a private jet wearing a black dress, a black bulletproof vest, a black mask, and her right arm in a black sling as she mourned for President Jovenel Moïse, who was killed July 7 at their private home. Some experts—like many in this country of more than 11 million people—were surprised at how quickly she reappeared in Haiti and questioned whether she plans to become involved in the country’s politics. “The fact that she returned could suggest she intends to play some role,” said Laurent Dubois, a Haiti expert and Duke University professor. “She may intervene in one way …