A 28-year-old woman presents with a 2-week history of progressive dysphagia and throat discomfort. She denies any acute aspiration event. On examination, the larynx appears normal on indirect laryngoscopy, but she has persistent symptoms. Imaging is suspected to rule out a radiolucent foreign body or other pathology. Which investigation is most appropriate for visualizing a non-radiopaque foreign body in the hypopharynx and cervical esophagus?