A 2-year-old girl from Mumbai is brought to the ENT clinic with a painless neck mass along the anterior border of the sternocleidomastoid muscle at the angle of the mandible. Ultrasound shows a cystic lesion with a thin wall. The parents report that the mass has been present since birth and occasionally drains a clear, odorless fluid. Which pharyngeal pouch is the embryological origin of this lesion?