A 32-year-old woman of Indian origin presents with a 1-week history of gross hematuria, facial puffiness, and dyspnea on exertion. Blood pressure is 162/104 mmHg. She denies recent infections or rashes. Urinalysis shows 4+ blood, RBC casts, and 2.5 g/day proteinuria. Serum creatinine is 2.1 mg/dL (baseline unknown). C3 and C4 levels are normal. ANA and anti-GBM antibodies are negative. Renal ultrasound shows normal-sized kidneys. What is the most likely diagnosis?