agents get a kickoff inbox message on start/restart/rebuild

new Coordinator::kick_agent(name, reason) drops a system message
into the agent's inbox so the next turn picks it up with a 'you
were just (re)started, check /state/ for notes, --continue session
is intact' hint. wakes the turn loop without any harness-side
handling needed — it's just another inbox message with sender =
'system'.

wired from:
- dashboard /start /restart /rebuild handlers (via lifecycle_action's
  on-success tail)
- manager mcp_hyperhive_start / restart

dashboard: pending approvals + tombstones + questions now refresh on
a 5s heartbeat when nothing else is happening. previously refresh
only fired on async-form submit or on broker traffic addressed to
operator — manager-queued approvals went through neither, so the
operator had to reload to see them. 5s is the slow-path; 2s
remains for in-flight transients.

hive-c0re/assets/app.js

@@ -397,10 +397,14 @@
       renderQuestions(s);
       renderInbox(s);
       renderApprovals(s);
-      // Auto-refresh while a spawn is in flight OR while any container
-      // has a pending lifecycle action; otherwise back off.
+      // Auto-refresh: fast (2s) while a spawn or a per-container
+      // action is in flight, otherwise heartbeat (5s) so newly-queued
+      // approvals from the manager show up without the operator
+      // having to reload the page. Broker SSE already triggers a
+      // refresh on operator-bound messages; this catches the rest
+      // (approvals, tombstones, questions).
       const anyPending = s.containers.some((c) => c.pending);
-      const next = (s.transients.length || anyPending) ? 2000 : 0;
+      const next = (s.transients.length || anyPending) ? 2000 : 5000;
       if (pollTimer) { clearTimeout(pollTimer); pollTimer = null; }
       if (next) pollTimer = setTimeout(refreshState, next);
     } catch (err) {