Pancreatic Cancer Double-Duct Sign

A 68-year-old man with a 40-pack-year smoking history and newly diagnosed type 2 diabetes presents with progressive painless jaundice, dark urine, pale stools, and 9 kg weight loss over 6 weeks. Examination reveals scleral icterus, a palpable non-tender distended gallbladder, and excoriations from pruritus. CA 19-9 is markedly elevated at 1,850 U/mL. Multiphasic contrast-enhanced CT of the abdomen is shown. The structure marked **A** in the diagram represents a hypoenhancing mass in the pancreatic head with ill-defined infiltrative margins. Based on the clinical presentation, imaging findings (including the double-duct sign), and the hypoattenuating nature of the structure marked **A**, what is the most likely diagnosis?