A 62-year-old woman with a 10-year history of hypertension presents with exertional chest pain and syncope. On examination, blood pressure is 160/70 mmHg with a narrow pulse pressure. A harsh, late-peaking systolic murmur is heard at the right upper sternal border, radiating to the carotids. There is a palpable systolic thrill at the aortic area. Echocardiography shows a bicuspid aortic valve with severe calcification, an aortic valve area of 0.6 cm², and concentric left ventricular hypertrophy with an ejection fraction of 45%. Which pathological process best explains the valve morphology and hemodynamic findings?