A 5-year-old girl from Delhi presents with progressive muscle weakness, myalgia, and dark urine after running in a school sports day 3 days ago. On examination, she has mild hepatomegaly and proximal muscle weakness. Serum creatine kinase is 8,500 U/L (normal <200), and urine myoglobin is positive. Her blood glucose during fasting is 85 mg/dL (normal). A forearm ischemic exercise test shows no rise in venous lactate but a normal rise in ammonia. Which glycogen storage disorder is most likely?