A 5-year-old girl from Mumbai is brought to the pediatric ward on day 6 of dengue fever. She had fever, rash, and mild hepatomegaly on days 1–5. Today, her fever has subsided, but she complains of abdominal pain and has vomited twice. On examination, she is alert, blood pressure 92/58 mmHg (normal for age), capillary refill 2 seconds, and mild abdominal distension with tenderness in the right upper quadrant. Laboratory results: WBC 2.8 × 10⁹/L, platelets 65 × 10⁹/L, hematocrit 42% (baseline 36%), AST 280 IU/L, ALT 160 IU/L, albumin 2.8 g/dL. Dengue NS1 antigen is positive. Abdominal ultrasound shows ascites and gallbladder wall thickening. What is the most likely diagnosis?