A 26-year-old female presents with recurrent oral ulcers and arthralgia for 2 years, accompanied by photosensitivity. Two weeks ago, she developed bilateral lower extremity edema. Laboratory tests: Urinalysis shows proteinuria (+++), RBCs 10-20/HP, and ANA(+). Renal biopsy pathology reveals mild mesangial cell and matrix proliferation, endothelial cell proliferation, subendothelial and subepithelial eosinophilic deposits, and partial crescent formation. Immunofluorescence: IgA(++), IgG(+++), IgM(+++), C1q(++), C3(++). The diagnosis is: