A 42-year-old man from Delhi presents with a 2-month history of palpitations, tremor, heat intolerance, and weight loss of 6 kg despite increased appetite. On examination, he is anxious, has a resting heart rate of 108 bpm with a fine tremor, warm moist skin, and a diffusely enlarged, firm, non-tender thyroid gland. His eyes appear prominent with lid lag and lid retraction. Laboratory tests show: TSH <0.01 mIU/L (normal 0.4–4.0), free T4 8.2 ng/dL (normal 0.8–1.8), free T3 6.8 pg/mL (normal 2.3–4.2), and TSH receptor antibodies (TRAb) positive. What is the primary mechanism by which TSH receptor antibodies cause thyroid hormone excess in this patient?