A 58-year-old female patient presents with progressively worsening xerostomia and fatigue over the past year. Physical examination reveals multiple dental caries, residual black tooth roots, and generalized lymphadenopathy. Laboratory tests show ESR 89mm/h, serum γ-globulin 28.5%, ANA 1:80 positive, and anti-SSA antibody positive. The most likely diagnosis is: