A 10-month-old male is brought to the emergency department with a 12-hour history of severe, intermittent crying episodes. The infant pulls his legs to his chest during the episodes and appears lethargic between them. His mother reports one episode of vomiting, initially non-bilious but now greenish, and a single stool containing blood and mucus. On physical examination, his abdomen is mildly distended, and a sausage-shaped mass is palpated in the right upper quadrant. What is the most likely diagnosis?
