A 58-year-old woman with CKD stage 5 (eGFR 12 mL/min/1.73m²) on hemodialysis presents with fatigue and dyspnea. Hemoglobin is 8.2 g/dL, MCV 82 fL, serum iron 45 mcg/dL (normal 60–170), ferritin 850 ng/mL (normal 30–300), TSAT 18% (normal >20%), reticulocyte count 0.8% (normal 0.5–2.5%). She has been on erythropoietin-stimulating agent (ESA) for 6 months without improvement. What is the most appropriate next step in management?