Catherine, the Princess of Wales, said on Friday that she planned to take part in a parade on Saturday marking the birthday of King Charles III, a tentative return to the public stage after confirming in March that she was being treated for cancer. The news, which Catherine released in a highly personal six-paragraph statement, reflected both the progress she has made since she was first hospitalized for abdominal surgery last January and the long road to recovery she still faces. “I am...