A 60-year-old man with long-standing type 2 diabetes and hypertension has an eGFR of 45 mL/min/1.73 m² and urinary albumin:creatinine ratio of 15 mg/mmol. His blood pressure is 145/88 mmHg on amlodipine alone. What is the most appropriate additional medication to protect his kidneys and reduce cardiovascular risk?