Move native multi-agent topology rendering into Charts

Move the native multi-agent topology renderer, layout, hub, cards, metrics and activity strip from Sandbox UI to Charts. Sandbox UI492 keeps model/provider identity in a small wrapper and deletes its private engine; WorkflowGraph and run composition forward their live shared presentation helpers to this implementation. The ordinary React entry and static root retain their dependency boundaries. The new graph entry has optional React DOM/React Flow/ELK peers.

Run ID: run_6c3fee201ccc4bcad161c130f576beb5