A 32-year-old woman from Delhi presents 6 months after evacuation of a complete molar pregnancy. She was counselled on contraception and serial β-hCG monitoring. Her hCG levels were undetectable by 8 weeks post-evacuation and remained normal for 4 months. She now presents with a 2-week history of vaginal bleeding, mild dyspnea, and chest pain. Chest X-ray shows multiple bilateral pulmonary nodules. Serum β-hCG is 85,000 mIU/mL. What is the most likely diagnosis?