A 28-year-old female patient presents with recurrent low-grade fever, oral and vulvar ulcers for 1 year, accompanied by a red nodular rash on both lower limbs and arthralgia for 1 month. No nasal congestion or rhinorrhea. Reports cough, but no abdominal pain or diarrhea. ESR 40 mm/h, antinuclear antibody (ANA), anti-extractable nuclear antigen (anti-ENA), and antineutrophil cytoplasmic antibody (ANCA) all negative. The most likely diagnosis is: