A 28-year-old woman presents to the emergency department with a 16-hour history of periumbilical pain that migrated to the right lower quadrant. On examination, she has a positive Rovsing sign and McBurney's point tenderness. Her temperature is 38.2°C, HR 92/min, and WBC 12,500/μL. Urine pregnancy test is negative. Abdominal ultrasound shows a non-compressible appendix measuring 8 mm with surrounding free fluid. What is the most appropriate next step in management?