A 25-year-old man presents with hemoptysis, fatigue, and decreased urine output. He reports a 3-week history of persistent cough and dark-colored urine. Physical examination reveals mild dyspnea and bilateral inspiratory crackles on lung auscultation. Urinalysis shows hematuria, proteinuria, and red blood cell casts. Serum creatinine is elevated, and anti-GBM antibodies are positive. What is the most likely diagnosis?
