A 32-year-old man from Delhi presents with a 3-week history of fever, myalgia, and rash. He reports unprotected sexual contact 4 weeks ago. On examination, he has generalized lymphadenopathy and oral candidiasis. His CD4 count is 180 cells/μL. HIV ELISA is positive, and Western blot confirms HIV-1 infection. What is the most appropriate immediate next step in management?