A 35-year-old man of Indian origin presents with a 6-month history of progressive photosensitivity, blistering lesions on the dorsal surfaces of hands and forearms, and hyperpigmentation. He has a history of chronic hepatitis C infection diagnosed 3 years ago. On examination, fragile blisters and erosions are seen on sun-exposed areas; the skin over the knuckles shows scarring and milia. His liver function tests show mild elevation of transaminases (ALT 2× ULN). Urine porphyrin analysis shows marked elevation of uroporphyrin (420 μg/24h; normal <30 μg/24h) with normal or near-normal PBG levels. Which of the following is the most likely diagnosis?