A 28-year-old woman presents with fever, petechiae, and gum bleeding for 5 days. Blood smear shows 85% blasts with Auer rods. CBC: Hb 7.2 g/dL, WBC 45,000/µL, platelets 18,000/µL. PT is 18 sec (control 12), aPTT 52 sec (control 36), fibrinogen 80 mg/dL. What is the most appropriate immediate next step in management?