A 48-year-old man with a 6-month history of chronic rhinosinusitis presents with persistent nasal obstruction, postnasal drip, and recurrent facial pain despite 3 months of medical therapy (intranasal corticosteroids, saline irrigation, and two courses of antibiotics). Nasal endoscopy shows mucosal edema and polyps in the ostiomeatal complex. CT paranasal sinuses reveals pansinusitis with ostiomeatal complex obstruction. What is the most appropriate next step in management?