Overlap 120 peaked P@1 0.4667 / R@5 1.0 on our fixed size=400 FAQ — 160 diluted

Fixed RecursiveCharacterTextSplitter + chunk_size=400 on our RelayDesk FAQ (15 graded queries). Only swept chunk_overlap ∈ {0,40,80,120,160}. Not a Wave5 splitter/size A/B. Desk API: $0. overlap #c