A 28-year-old nulliparous woman presents with a 4-year history of severe cyclic pelvic pain, dyspareunia, and infertility. She reports that pain starts 3–4 days before her period and improves after menses ends. On examination, there are tender nodules palpable in the pouch of Douglas. Transvaginal ultrasound reveals multiple small cysts in both ovaries (largest 2 cm) with normal myometrial echotexture and a normal junctional zone. Diagnostic laparoscopy shows chocolate cysts on the ovaries and peritoneal implants. What is the most likely diagnosis?