A 48-year-old man from Mumbai presents with progressive muscle weakness, polyuria, and polydipsia for 6 months. On examination, he has central obesity, purple striae on the abdomen, and proximal muscle weakness (hip and shoulder girdle). Blood pressure is 162/98 mmHg. Laboratory findings: fasting glucose 185 mg/dL, serum potassium 3.1 mEq/L, 8 AM cortisol 28 µg/dL (normal 5–25 µg/dL), and ACTH 68 pg/mL (normal 10–50 pg/mL). A low-dose dexamethasone suppression test (1 mg overnight) shows cortisol 24 µg/dL (normal <1.8 µg/dL). What is the most likely diagnosis?