A 38-year-old man from Mumbai presents with 6 months of progressive fatigue, muscle weakness, and weight gain despite anorexia. He has central obesity, proximal myopathy, and hypertension (162/104 mmHg). Laboratory findings: morning cortisol 32 µg/dL, 24-hour urinary free cortisol 320 µg/day, ACTH 68 pg/mL (normal 10–46), and plasma potassium 3.1 mEq/L (normal 3.5–5.0). A low-dose dexamethasone suppression test (LDDST) shows cortisol of 22 µg/dL. A high-dose dexamethasone suppression test (HDDST) shows cortisol of 8 µg/dL. Pituitary MRI is normal. What is the most likely diagnosis?