A 52-year-old postmenopausal woman from Mumbai presents with a 2 cm hard, irregular mass in the upper outer quadrant of the left breast discovered on self-examination 3 weeks ago. Physical examination reveals a fixed mass, skin dimpling, and a single ipsilateral axillary lymph node (1.5 cm, firm, mobile). Mammography confirms a BIRADS 5 lesion. Core needle biopsy shows invasive ductal carcinoma with intermediate grade (Nottingham score 6/9). Staging investigations including chest X-ray, abdominal ultrasound, and bone scan are normal. The patient is counselled for surgery. Which of the following is the most appropriate surgical management?