A 35-year-old woman with a 4 cm solitary thyroid nodule undergoes fine-needle aspiration cytology (FNAC) showing Bethesda Category IV (atypia of undetermined significance). She opts for surgery. Intraoperatively, the nodule appears confined to the left lobe with no gross extrathyroidal extension, and ipsilateral lymph nodes are not enlarged. Which of the following represents the most appropriate surgical approach according to current ATA guidelines?