A 60-year-old female with a 5-year history of diabetes mellitus (DM) presents with bilateral lower extremity edema for 1 year. Physical exam: BP 160/80 mmHg, heart rate 80 bpm, regular rhythm, clear breath sounds in both lungs, and pitting edema in both lower extremities. Urinalysis (UA) shows proteinuria (+++), RBCs 2-3/HP, and UTP 5g. Renal pathology: immunofluorescence IgG(+), IgA(-), IgM(-), C3(-), C1q(-), Alb(+), with linear IgG and Alb deposits along capillary walls. Light microscopy reveals 15 glomeruli with mild mesangial cell and matrix proliferation, segmental aneurysmal dilatation, and K-W nodules. The diagnosis is: