A 28-year-old woman presents with a recent episode of coughing up some blood, frequent nosebleeds, and now decreased urine output. A nasal mucosa ulcer was seen on inspection. Her urinalysis is positive for protein and red cells consistent with a GN. The CXR shows two cavitary lesions and her serology is positive for antineutrophil cytoplasmic antibodies (ANCA). Which of the following is the most likely diagnosis?