A 60-year-old woman with type 2 diabetes and a prior ST-elevation myocardial infarction 1 year ago is taking metformin 1000 mg twice daily. Her A1c is 8.2%, BMI is 32 kg/m², eGFR is 65 mL/min/1.73 m², and blood pressure and lipids are at goal. Which is the most appropriate next step to both improve glycemic control and reduce cardiovascular risk?