A 58-year-old man with type 2 diabetes mellitus and chronic kidney disease (eGFR 22 mL/min/1.73m²) presents to the emergency department with palpitations and muscle weakness. His wife reports he consumed a high-potassium diet (bananas, oranges, tomato juice) over the past 2 days. On examination, blood pressure is 148/92 mmHg, heart rate 102 bpm. Laboratory investigations reveal: serum potassium 7.2 mEq/L, serum creatinine 3.8 mg/dL, pH 7.28, HCO₃⁻ 16 mEq/L. ECG shows peaked T waves and prolonged PR interval. What is the most appropriate immediate intervention?