DagView no longer has a DAG-level agent, so consumers derive it from the
per-node agents:
- hivectl dag_progress.rs: dag_agents(d) helper (distinct node agents,
comma-joined) in place of d.agent.
- dashboard builds.js: entryAgents(entry) helper likewise for the
rebuild-queue card + live-log header + cancel confirms.
- docs/coordinator.md: lease prose (node-agent-keyed, global per agent),
wire shape (NodeView.agent, no DagView.agent), and dropped the removed
dedup section.
e2b48d2014