A 22-year-old unmarried woman from Delhi presents with a 3-month history of progressive abdominal distension and mild left lower abdominal pain. On examination, she appears anxious and has a palpable left adnexal mass. Serum β-hCG is 45,000 mIU/mL (normal <5), AFP is 8,500 ng/mL (normal <10), and LDH is elevated at 680 U/L. Pelvic ultrasound shows a 12 cm heterogeneous left ovarian mass with cystic and solid components. What is the most likely diagnosis?