A 62-year-old woman with a history of recurrent cholangitis presents with fever (38.5°C), right upper quadrant pain, and jaundice. Laboratory tests show bilirubin 7.4 mg/dL, alkaline phosphatase 380 IU/L, and WBC 14,200/μL. Abdominal ultrasound reveals dilated intrahepatic bile ducts with multiple echogenic foci within the ducts, a normal-caliber common bile duct, and a normal gallbladder. What is the most likely diagnosis, and what is the immediate management priority?