A 58-year-old man from Bangalore is found to have serum calcium 7.8 mg/dL (normal 8.5–10.2), serum phosphate 5.2 mg/dL (normal 2.5–4.5), and intact PTH 8 pg/mL (normal 10–65) on routine screening. He is asymptomatic. Serum magnesium is 1.6 mg/dL (normal 1.7–2.2). Serum albumin is 4.0 g/dL. Renal function is normal (creatinine 0.9 mg/dL). Vitamin D level is 32 ng/mL (normal >30). What is the most likely diagnosis?