A 58-year-old woman with a 10-year history of type 2 diabetes mellitus presents with progressive edema, dyspnea, and a 3 kg weight gain over 2 weeks. Blood pressure is 142/92 mmHg. Serum creatinine is 2.8 mg/dL (eGFR 22 mL/min/1.73 m²), and urinary albumin-to-creatinine ratio is 380 mg/g. Serum potassium is 5.8 mEq/L. She is not on any ACE inhibitor or ARB. Which of the following best explains the hyperkalemia in the context of her declining renal function and RAAS physiology?