A 52-year-old man with a 10-year history of type 2 diabetes mellitus on metformin 1000 mg BD presents for routine follow-up. His current fasting blood glucose is 156 mg/dL, postprandial glucose 210 mg/dL, and HbA1c 8.1%. BMI is 28 kg/m², blood pressure 138/88 mmHg. Serum creatinine is 1.1 mg/dL (eGFR 68 mL/min/1.73m²). C-peptide is 2.8 ng/mL. He has no symptoms of heart failure, and echocardiography shows normal ejection fraction. Which agent should be added to metformin to reduce cardiovascular and renal mortality in this patient?