A 62-year-old postmenopausal woman from Delhi presents with acute back pain following a minor fall while gardening. She reports progressive loss of height (5 cm over 3 years) and increasing kyphosis. On examination, she is afebrile, height 152 cm, BMI 24 kg/m². Vertebral tenderness is present at T12–L1. Plain radiographs show a wedge-shaped compression fracture of L1 with loss of vertebral body height. Serum calcium 8.8 mg/dL, phosphate 3.5 mg/dL, alkaline phosphatase 68 U/L, 25-OH vitamin D 28 ng/mL. DEXA scan shows T-score of −2.8 at the lumbar spine and −2.5 at the femoral neck. What is the most likely diagnosis?