Replace ASCII-art diagrams across the README and docs/ with editable
.drawio sources plus exported PNGs, so the diagrams render clearly in
rendered markdown and can be maintained/regenerated instead of being
hand-edited as fragile text art. Non-diagram blocks (code, folder
trees, UI wireframes) were left as text.
Per-instance address override + live ClusterClient-based browse via a new
IBrowsableDataConnection capability on RealOpcUaClient. Lazy-loaded tree
with manual-paste fallback; offline-safe.