A 68-year-old man with long-standing type 2 diabetes and hypertension is found to have eGFR 48 mL/min/1.73 m² and an albumin–creatinine ratio (ACR) of 45 mg/mmol on two separate occasions. His blood pressure is 144/86 mmHg on Amlodipine alone. What is the most appropriate additional treatment to slow progression of kidney disease?