feat: host heartbeat status and dashboard metrics (2.2)

Track agent.heartbeat and report.daily.ssh per host; show online/stale
on Hosts UI; dashboard counters and SAC_HEARTBEAT_STALE_MINUTES config.

frontend/src/views/HostsView.vue

@@ -12,6 +12,9 @@
           <th>Product</th>
           <th>OS</th>
           <th>IPv4</th>
+          <th>Агент</th>
+          <th>Heartbeat</th>
+          <th>Отчёт</th>
           <th>Last seen</th>
           <th>Events</th>
         </tr>
@@ -23,6 +26,9 @@
           <td>{{ h.product }} {{ h.product_version || "" }}</td>
           <td>{{ h.os_family }}</td>
           <td>{{ h.ipv4 || "—" }}</td>
+          <td :class="'agent-' + h.agent_status">{{ agentLabel(h.agent_status) }}</td>
+          <td>{{ h.last_heartbeat_at ? formatDt(h.last_heartbeat_at) : "—" }}</td>
+          <td>{{ h.last_daily_report_at ? formatDt(h.last_daily_report_at) : "—" }}</td>
           <td>{{ formatDt(h.last_seen_at) }}</td>
           <td>{{ h.event_count ?? 0 }}</td>
         </tr>
@@ -43,6 +49,12 @@ function formatDt(iso: string) {
   return new Date(iso).toLocaleString("ru-RU");
 }
 
+function agentLabel(status: string) {
+  if (status === "online") return "online";
+  if (status === "stale") return "stale";
+  return "unknown";
+}
+
 onMounted(async () => {
   loading.value = true;
   try {