A 52-year-old man from Delhi presents to the neurology clinic with a 3-month history of severe, lancinating pain in the right cheek and upper jaw. The pain is triggered by touching his face, chewing, or exposure to cold wind, and lasts 15–30 seconds per episode. He has tried topical analgesics without relief. Neurological examination reveals normal facial sensation and motor function. MRI brain with contrast is normal. Which is the most likely diagnosis?