A 52-year-old man from Mumbai presents with progressive proximal muscle weakness, easy bruising, and facial plethora over 6 months. His wife notes he has become irritable and forgetful. Blood pressure is 162/98 mmHg. Laboratory findings: fasting glucose 156 mg/dL, sodium 142 mEq/L, potassium 3.1 mEq/L, 24-hour urinary free cortisol 285 μg/day (normal <50), and morning ACTH 68 pg/mL (normal <50). An overnight low-dose dexamethasone suppression test (1 mg) shows cortisol 22 μg/dL (suppression occurs at <5 μg/dL). A high-dose dexamethasone suppression test (8 mg overnight) shows cortisol suppresses to 8 μg/dL. What is the most likely diagnosis?