A 28-year-old woman presents to the emergency department with a recent episode of coughing up some blood, frequent nosebleeds, and now decreased urine output. On physical examination, a nasal mucosa ulcer is seen on inspection and the remainder of the examination is normal. Her urinalysis is positive for protein and red cells consistent with acute glomerulonephritis (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?