A 28-year-old man from rural India presents with sudden onset hematuria and mild flank pain for 3 days. He reports a sore throat 2 weeks prior that resolved spontaneously. On examination, blood pressure is 148/92 mmHg (previously normal). Urinalysis shows 3+ blood, RBC casts, and mild proteinuria (0.8 g/day). Serum creatinine is 1.2 mg/dL (baseline 0.9 mg/dL). Complement C3 levels are normal. Throat culture is negative. What is the most likely diagnosis?