A 24-year-old man presents with 2 days of severe pain, tearing, and redness of his left eye. He reports photophobia and a foreign-body sensation. He has had a similar episode once before that resolved after receiving an “antiviral eye medication.” He does not wear contact lenses. Temperature is 37.0°C (98.6°F). Slit-lamp examination shows branching, linear epithelial defects of the cornea that stain with fluorescein and have terminal bulbs; small vesicular lesions are noted on the eyelid margin. Which of the following is the most likely diagnosis?