A 3-year-old boy from a tribal village in Chhattisgarh is brought to the primary health centre with a 2-week history of cough and fever. On examination, he is underweight (weight-for-age 60% of expected), has generalized lymphadenopathy, and a firm hepatosplenomegaly. Chest X-ray shows bilateral hilar lymphadenopathy. Mantoux test (5 TU) shows 18 mm induration at 72 hours. What is the most appropriate next step in management according to RCH and NTEP guidelines?