A 42-year-old woman from Delhi presents with acute right upper quadrant pain and tenderness for 6 hours. She reports fever (38.5°C), nausea, and vomiting. On examination, Murphy's sign is positive. Ultrasound abdomen shows a 1.8 cm stone in the gallbladder with wall thickening (4 mm), pericholecystic fluid, and no dilatation of the common bile duct. WBC is 12,500/μL with left shift. What is the most appropriate next step in management?