A 35-year-old woman from Delhi presents with a 6-month history of progressive cognitive decline, tremor, and personality changes. Her husband reports she has become irritable and withdrawn. On examination, she has a resting tremor, hyperreflexia, and positive Romberg sign. Pupillary examination shows irregular, dilated pupils that react better to accommodation than to light (Argyll Robertson pupils). Serum RPR is positive (1:32) and CSF VDRL is positive. CSF shows lymphocytic pleocytosis (80 cells/μL, predominantly lymphocytes) with elevated protein (120 mg/dL) and normal glucose. What is the most likely diagnosis?