A 38-year-old man presents to the emergency department with severe epigastric pain radiating to the back for 6 hours. He reports consuming alcohol heavily the previous night. On examination, temperature is 38.2°C, heart rate 110/min, blood pressure 100/65 mmHg. Abdomen is tender in the epigastrium with guarding. Laboratory investigations show: serum amylase 1200 U/L (normal <100), serum lipase 2400 U/L (normal <60), WBC 14,500/μL, glucose 280 mg/dL, calcium 7.2 mg/dL. Abdominal ultrasound shows pancreatic edema without gallstones. What is the most likely diagnosis and the primary pathogenic mechanism?