A 58-year-old woman presents with a 4-week history of rapid enlargement of a mass in the left parotid region, accompanied by pain, facial nerve paralysis (House-Brackmann Grade III), and skin erythema. Ultrasound shows a heterogeneous, hypoechoic mass with ill-defined margins. FNAC reveals malignant cells consistent with mucoepidermoid carcinoma. What is the most appropriate next step in management?