A 32-year-old woman from Mumbai presents with secondary infertility of 2 years duration. She reports severe dysmenorrhea since her last delivery 4 years ago, which has progressively worsened. She also complains of chronic pelvic pain and deep dyspareunia. Her menstrual cycles are regular (28–30 days) but heavy. On examination, the uterus is fixed, retroverted, and tender. Transvaginal ultrasound shows multiple hypoechoic lesions in the myometrium with heterogeneous echotexture. What is the most likely diagnosis?