A 3-year-old boy from Delhi presents with severe hypoglycemia (blood glucose 35 mg/dL) and hepatomegaly during a routine clinic visit. His mother reports he becomes irritable and sweaty if meals are delayed by 2–3 hours. Physical examination reveals a protuberant abdomen with a firm, enlarged liver extending 8 cm below the costal margin. Serum lactate is elevated at 6 mmol/L (normal <2). Liver biopsy shows glycogen accumulation with normal structure. Which glycogen storage disorder is most likely?