A 55-year-old male presents to the emergency department with a 3-day history of worsening right upper quadrant pain, chills, and intermittent fever up to 39.5°C. He has a known history of chronic cholelithiasis and a prior episode of mild ascending cholangitis treated conservatively three months ago, which resolved with oral antibiotics. On examination, he appears acutely ill, is tachycardic (105 bpm), and has significant tenderness and guarding in the right upper quadrant. His sclerae show a mild icteric tinge. Initial blood work reveals a white blood cell count of 18,500/µL with a left shift, C-reactive protein of 180 mg/L, total bilirubin of 51.3 µmol/L, and alkaline phosphatase of 280 U/L. An urgent abdominal ultrasound shows cholelithiasis, a dilated common bile duct (12 mm), and a 6.5 cm hypoechoic lesion in the right hepatic lobe with internal septations. Considering his evolving clinical picture and the new sonographic findings, what is the most likely diagnosis and the definitive initial management strategy?