A 38-year-old woman from rural Maharashtra presents with progressive bone pain, muscle weakness, and recurrent fractures over the past 2 years. She reports minimal sun exposure due to cultural practices and a predominantly cereal-based diet low in dairy. On examination, she has diffuse bone tenderness and proximal muscle weakness. Serum calcium is 7.8 mg/dL (normal 8.5–10.5), phosphate 2.1 mg/dL (normal 2.5–4.5), alkaline phosphatase 156 U/L (normal 30–120), and 25-hydroxyvitamin D is 12 ng/mL (normal >30). X-ray of the pelvis shows Looser's zones. What is the most likely diagnosis?