**A 29-yeаr-оld wоmаn with а histоry HIV presents with gradual onset of shortness of breath, nonproductive cough, and low-grade fever over the past 10 days. She is taking antiretroviral therapy. On examination, lung auscultation is relatively normal, but her oxygen saturation is low. A chest CT scan shows diffuse, bilateral ground-glass opacities. Which of the following is the most likely diagnosis?