A 24-year-old woman presents with abdominal pain, joint discomfort, and lower limb rash. She was well until 1 week before presentation. On examination, she has a palpable purpuric rash on her legs, nonspecific abdominal discomfort, and no active joints. She has 3+proteinuria, normal WBC, no eosinophils, and elevated creatinine of 1.6 mg/dL. Biopsy of the rash confirms vasculitis with immunoglobulin A (IgA) 3+and C3 (complement 3) deposition on immunofluorescence.For the above patient with vasculitis syndrome, select the most likely diagnosis.