A 3-year-old boy from Tamil Nadu presents with progressive hepatosplenomegaly, developmental delay, and recurrent respiratory infections over the past 18 months. On examination, he has coarse facial features, corneal clouding, and a palpable spleen 8 cm below the costal margin. Bone marrow aspirate shows foamy macrophages. Serum acid phosphatase is markedly elevated. What is the most likely diagnosis?