feat(syslog): lines beside the readings: around an anomaly, in get_anomaly, and marked on host and SNMP charts (#6002)

get_anomaly's circumstances gain the host's or SNMP device's syslog
warnings and worse (mcp_events / mcp_resource_events). An anomaly row opens
"Syslog around it", read only when opened. A shared Chart.js plugin
(chart-marks.js) draws a dashed line at each syslog error on the host
metrics charts and an SNMP device's charts, with a line saying how many.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/host_agent/templates/host_detail.html

@@ -42,6 +42,7 @@
   </div>
   {% endif %}
 </div>
+{% if "syslog" in enabled_plugins %}<p id="hm-marks-note" class="field-hint" hidden style="margin:0.5rem 0 0;"></p>{% endif %}
 {# Hidden poller: fetches the history series and applies it to the charts above
    (no visible swap). Lazy on load → never blocks paint; refreshed slowly + on
    range change. #}
@@ -112,6 +113,11 @@
       ch.update("none");
     }
     if (rangeKey) document.querySelectorAll(".hm-chart-range").forEach((s) => { s.textContent = rangeKey; });
+    {% if "syslog" in enabled_plugins %}
+    // The host's own syslog errors over the same span (#6002).
+    stewardMarkCharts("/plugins/syslog/marks?host_id={{ host.id }}&range=" + encodeURIComponent(rangeKey || ""),
+                      Object.values(charts), document.getElementById("hm-marks-note"));
+    {% endif %}
   };
 })();
 </script>