feat(#2591): hive-jobq Node lifecycle — started/finished timestamps + failure reason

Node gains started_at/finished_at (chrono DateTime<Utc>, serialized
RFC 3339 on the wire per hive_sh4re::wire_time) plus error (String).
Graph::set_state self-stamps started_at on the first Running transition
and finished_at on the first terminal one, via an internal now_utc()
clock (keeps settle/complete signatures stable). Outcome::Failed(String)
carries the failure reason, set on the terminal transition.

hive-c0re complete_node builds Outcome::Failed(msg); its node_rt
side-table stays i64 for now (double-write) until #2637 reads the Node.

Toward #2637: the jobq graph becomes the source of truth for per-node
lifecycle so the queue can be sent to the client as-is.

hive-c0re/src/job_queue/mod.rs

@@ -408,7 +408,13 @@ impl JobQueue {
         let now = now_unix();
         let (error, outcome) = match result {
             Ok(()) => (None, Outcome::Done),
-            Err(e) => (Some(truncate_error(&e)), Outcome::Failed),
+            Err(e) => {
+                // The reason rides the crate `Outcome::Failed` (stamped onto the
+                // graph `Node`); the `node_rt` copy stays for now until the wire
+                // reads it off the node directly.
+                let msg = truncate_error(&e);
+                (Some(msg.clone()), Outcome::Failed(msg))
+            }
         };
         if let Some(rt) = inner.node_rt.get_mut(&node_id) {
             rt.finished_at = Some(now);