A 38-year-old Indian woman presents with a 3-month history of progressive abdominal distension and early satiety. On examination, she has a palpable left upper quadrant mass and mild hepatomegaly. Laboratory investigations show hemoglobin 9.2 g/dL, WBC 7,200/μL, and platelets 1,20,000/μL. Abdominal CT reveals a large splenic mass (12 cm) with involvement of para-aortic lymph nodes. Bone marrow biopsy shows infiltration by large cells with "wrinkled tissue paper" appearance and positive CD20, CD5, and FMC7 markers. What is the most likely diagnosis?