A 55-year-old woman with heart failure with reduced ejection fraction (HFrEF, EF 30%) on lisinopril and carvedilol presents with worsening dyspnea, orthopnea, and a 3 kg weight gain over 2 weeks. Physical exam shows elevated JVP, bilateral crackles, and peripheral edema. Serum sodium 128 mEq/L (normal 135–145), potassium 5.8 mEq/L (normal 3.5–5.0), creatinine 1.4 mg/dL (baseline 1.0). What is the most appropriate next step in management?