hive-c0re: finish chrono-clock migration

hive-c0re/src/job_queue/model.rs

@@ -12,6 +12,7 @@
 //! DAG can span agents). See `docs/coordinator.md::Job queue` for the
 //! full design.
 
+use chrono::{DateTime, Utc};
 pub use hive_host_sock::jobs::{DagView, NodeId, PermPayload, Source, State};
 use serde::Serialize;
 
@@ -283,7 +284,7 @@ pub enum NodeKind {
     Dag {
         source: Source,
         reason: String,
-        created_at: i64,
+        created_at: DateTime<Utc>,
     },
 }