A 32-year-old woman presents with severe anal pain during and after defecation for the past 3 weeks. She reports bright red blood on toilet paper and describes the pain as sharp and burning, lasting 1–2 hours after each bowel movement. On examination, a visible tear is noted in the posterior midline of the anal canal. Digital rectal examination is extremely painful and cannot be completed. She denies fever, perianal discharge, or a history of inflammatory bowel disease. What is the most likely diagnosis?