Pediatric surgical emergencies: Meckel's diverticulum and intussusception

An 8-week-old male infant born to non-consanguineous parents presents with a 1-week history of intermittent abdominal distension, failure to thrive, and explosive diarrhoea. On examination, the infant appears malnourished with visible peristaltic waves. Abdominal examination reveals a palpable mass in the right upper quadrant. Plain abdominal radiograph shows dilated small bowel loops with air-fluid levels. Contrast-enhanced CT abdomen reveals a transition point at the ileocaecal junction with proximal small bowel dilatation. The infant's mother reports that the child has been feeding well until the onset of symptoms. Which of the following is the most likely diagnosis?