Human-in-the-loop status for a workflow execution

Reported whether an execution was paused, in memory, awaiting human approval. The multi-agent execute routes pause nothing since v11.1.0 (#4382), and the in-memory engine this route read is retired (#4249), so every id answers 404 Execution not found. A multi-agent step is held only in confirm or step mode; read its approval state through the workflow control plane. The route is removed in v12.0.0.