A 28-year-old man from rural Maharashtra presents with progressive darkening of urine over the past 2 years, which turns black on standing or exposure to air. He has recently noticed dark pigmentation in the cartilage of his ears and sclera. Serum uric acid is elevated at 8.2 mg/dL. Urine chromatography shows elevated homogentisic acid. Serum phenylalanine and branched-chain amino acids are normal. What is the most likely diagnosis?