A 4-week-old, exclusively breastfed infant whose parents declined all newborn medications presents with sudden onset of seizures. On examination, the fontanelle is bulging. A head CT confirms an intracranial hemorrhage. Coagulation studies reveal a markedly prolonged prothrombin time (PT), a slightly prolonged partial thromboplastin time (PTT), and a normal platelet count. What is the most likely diagnosis?