A 52-year-old postmenopausal woman from Delhi presents with a 3-month history of a painless, hard lump in the upper outer quadrant of her right breast. On examination, the mass is 2 cm, fixed to the chest wall, with overlying skin dimpling and a positive Peau d'orange appearance. Axillary lymph nodes are palpable and hard. Mammography shows a stellate lesion with microcalcifications. Core needle biopsy reveals invasive ductal carcinoma with intermediate nuclear grade. Immunohistochemistry shows ER+, PR+, HER2−. What is the most appropriate next step in management?