A 28-year-old woman from Mumbai, known to be HIV-positive with CD4 count 120 cells/μL, presents with a 2-week history of progressive headache, fever, and neck stiffness. She denies photophobia. On examination, she is alert but has mild neck rigidity. CSF analysis shows: protein 180 mg/dL, glucose 25 mg/dL (serum glucose 95 mg/dL), WBC 85 cells/μL (90% lymphocytes), negative Gram stain, negative bacterial culture, and negative India ink preparation. What is the most likely diagnosis?