A 62-year-old woman from Delhi presents with a 6-week history of left-sided abdominal pain and altered bowel habits. Colonoscopy reveals a 4 cm ulcerated mass in the sigmoid colon. Biopsy confirms moderately differentiated adenocarcinoma. CT staging shows the tumour invading the muscularis propria without breaching the visceral peritoneum, and no regional lymph nodes >1 cm are identified (T2N0M0). She has no comorbidities and is keen for curative surgery. What is the most appropriate surgical procedure?