A 46-yeаr-оld mаle presents with аcute rectal pain that began suddenly 2 days agо after straining during a bоwel movement. He describes severe, constant pain that makes sitting uncomfortable. He denies fever, abdominal pain, or changes in bowel habits. He reports a history of intermittent painless bright red blood on toilet paper in the past. On examination, there is a 2-cm, tense, bluish, exquisitely tender nodule at the anal verge. No purulent drainage is noted. Digital rectal exam is deferred due to pain. Which of the following is the most likely diagnosis?