A 52-year-old man with a 10-year history of type 2 diabetes mellitus presents with progressive bilateral ankle edema, foamy urine, and dyspnea on exertion for 2 months. His blood pressure is 158/94 mmHg. Laboratory investigations reveal: serum creatinine 2.8 mg/dL, blood urea 68 mg/dL, serum albumin 2.4 g/dL, 24-hour urine protein 6.5 g, serum sodium 132 mEq/L, potassium 5.8 mEq/L. Urinalysis shows 3+ proteinuria, 2+ hematuria, and occasional hyaline casts. Renal ultrasound shows bilateral kidney size 9 cm with increased echogenicity. Serum complement C3 and C4 are normal. Which of the following is the most likely diagnosis?