A 2-year-old girl from rural Maharashtra is brought to the pediatric clinic by her mother with a 6-month history of poor weight gain and recurrent infections. On examination, she weighs 8 kg (expected 12–13 kg for age), has visible ribs and sparse hair, and shows bilateral pitting edema over the dorsum of feet. Her mother reports that the child eats mainly rice and lentils, with rare access to milk or eggs. Laboratory investigations show: hemoglobin 9.2 g/dL, serum albumin 2.1 g/dL (normal >3.5), and total serum protein 4.8 g/dL. What is the most likely diagnosis?