A 48-year-old woman presents to the emergency department with acute right upper quadrant pain, fever (38.5°C), and jaundice. Murphy's sign is positive. Ultrasound shows a thickened gallbladder wall, pericholecystic fluid, and a 2 cm stone impacted in the cystic duct. Serum bilirubin is 4.2 mg/dL, ALT 320 U/L, ALP 180 U/L. What is the most appropriate next step in management?