A 22-year-old male presents to the emergency department with a 24-hour history of periumbilical pain that has shifted to the right lower quadrant. He reports anorexia, nausea, and one episode of vomiting. On examination, he is febrile (38.2°C), and tenderness is maximal at McBurney's point with rebound tenderness and guarding. Rovsing's sign is positive. White blood cell count is 12,500/mm³ with left shift. Abdominal ultrasound shows a non-compressible, dilated appendix measuring 8 mm with surrounding free fluid. What is the most appropriate next step in management?