A 4-year-old boy from Delhi presents with a 3-week history of fever, pallor, and easy bruising. On examination, he is febrile (38.5°C), has hepatosplenomegaly, and petechial rash on lower limbs. Complete blood count shows hemoglobin 7.2 g/dL, WBC 85,000/μL with 65% blasts, and platelets 35,000/μL. Bone marrow aspiration reveals >90% lymphoblasts with cytoplasmic vacuoles and Auer rods. Flow cytometry is pending. What is the most likely diagnosis?