A 38-year-old female patient has recurrent oral ulcers for 10 years, alternating episodes of iritis for 3 years, and vulvar ulcers with lower back and lower limb pain for the past 3 months. Physical examination shows scattered ulcers on bilateral buccal mucosa, heart rate 80 bpm with regular rhythm, and left sacroiliac joint tenderness (+). The most likely diagnosis is: