A South Florida bank has become the first from the United States to sign a correspondent banking relationship in Cuba, a potential boost for U.S.-Cuban commerce following newly restored diplomatic relations between the longtime adversaries. Stonegate Bank, which earlier this year became the Cuban government’s bank for its diplomatic mission in the United States, signed a deal with Cuba’s Banco Internacional de Comercio S.A. on Tuesday, a day after the United States and Cuba re-established diplomatic ties that had been severed for 54 years.