A 32-year-old male with a history of rheumatoid arthritis on oral steroid therapy presents with worsening fever, chest pain, and dyspnea over 15 days. Pleural fluid is straw-colored, Rivalta test (+), specific gravity 1.024, WBC 300×10<sup>6</sup>/L (lymphocytes 60%). Chest X-ray shows moderate right pleural effusion and right hilar lymphadenopathy. The most likely diagnosis is: