feat(#2591): add NodeKind::Dag DAG-container variant

hive-c0re/src/job_queue/exec.rs

@@ -103,6 +103,10 @@ pub(super) async fn run_node(coord: &Arc<Coordinator>, claim: &Claim) -> Result<
         NodeKind::ResolveApproval => run_resolve_approval(coord, claim).await,
         NodeKind::EmitRebuilt => Ok(run_emit_rebuilt(coord, claim)),
         NodeKind::RevertIntent => run_revert_intent(coord, claim).await,
+        // Pure grouping container — no work; completing it lets it reach
+        // `Finishing` so its child template nodes start. The DAG's terminal
+        // hook fires when the container itself rolls up terminal.
+        NodeKind::Dag { .. } => Ok(NodeOutput::default()),
     }
 }