A 42-year-old woman from Delhi presents with progressive central obesity, proximal muscle weakness, and easy bruising for 8 months. On examination, she has a moon facies, supraclavicular fat pads, and purple striae on the abdomen. Blood pressure is 156/98 mmHg. Laboratory investigations show: 24-hour urinary free cortisol 285 µg/day (normal <50), morning plasma cortisol 28 µg/dL, and ACTH 8 pg/mL (normal 10–46). A low-dose dexamethasone suppression test (LDDST) shows cortisol of 18 µg/dL after 1 mg dexamethasone. What is the most likely diagnosis?