A 16-year-old boy presents to the ENT clinic with a 6-month history of progressive unilateral nasal obstruction and recurrent epistaxis. His mother reports he has been experiencing postnasal drip and occasional otalgia. On examination, a smooth, reddish mass is visible in the nasopharynx, and there is blood-stained nasal discharge. Contrast-enhanced CT shows a highly vascular mass in the nasopharynx with widening of the pterygopalatine fossa and erosion of the pterygoid plates. What is the most likely diagnosis?