A 4-year-old boy from Delhi presents with a 3-week history of fever, pallor, and petechiae. On examination, he has hepatomegaly (3 cm below costal margin) and splenomegaly (4 cm). Complete blood count shows hemoglobin 7.2 g/dL, WBC 85,000/μL with 70% blasts, and platelets 35,000/μL. Peripheral blood smear confirms acute leukemia with Auer rods. What is the most appropriate next step in management?