A 58-year-old man from rural Maharashtra presents with progressive fatigue and dyspnea on exertion for 6 months. He has a 12-year history of type 2 diabetes mellitus (HbA1c 9.2%) and hypertension (BP 158/94 mmHg on amlodipine 5 mg daily). Serum creatinine is 2.8 mg/dL (baseline 0.9 mg/dL 2 years ago), eGFR 22 mL/min/1.73m², urine protein-to-creatinine ratio 2.4 g/g, and hemoglobin 8.9 g/dL. Urinalysis shows 3+ proteinuria and no active sediment. What is the most appropriate next step in management to slow CKD progression?