A 3-day-old male neonate born to an O-positive mother presents with severe jaundice. The mother is O-positive and the baby is B-positive. Antenatal blood group serology showed maternal indirect Coombs test (ICT) negative. Postnatal investigations: total serum bilirubin 18 mg/dL, direct bilirubin 0.8 mg/dL, hemoglobin 14 g/dL, reticulocyte count 8%, peripheral smear shows spherocytes. Direct Coombs test (DCT) on baby's blood is positive. What is the most likely diagnosis?