A 52‑year‑old man presents with a 12‑hour history of severe epigastric pain radiating to the back, worse lying flat, improved by leaning forward. He has nausea and vomiting. Serum lipase is 1 200 U/L (normal <60 U/L), ALT 45 U/L, triglycerides 1.5 mmol/L and serum calcium 2.30 mmol/L. Ultrasound shows gallstones with no dilated bile ducts. According to evidence‑based management of acute pancreatitis, which is the most appropriate immediate management strategy?