LONDON — “Her office was like something out of Black Mirror,” recalls a young official of her first trip to see the woman now leading Britain’s civil service. Wherever she looked in Antonia Romeo’s old sanctum at the Department for International Trade, Romeo’s face smiled back. “It was covered in pictures of her with famous people,” the footballer David Beckham among them, the official recalled. “I couldn’t concentrate on the meeting, because I was just looking at the wall thinking, ‘is that