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>

steward/templates/_anomaly.html

@@ -68,5 +68,14 @@ Held {{ metric_value(a.metric_name, a.peak_level) }}; usual for that hour
     {{ anomaly_when(v) }} · {{ anomaly_level(a) }}
   </div>
   <div style="font-size:0.8rem;color:var(--text-muted);margin-top:0.2rem;">{{ anomaly_review(a, back) }}</div>
+  {%- if "syslog" in enabled_plugins and v.last_span %}
+  {#- The device's own log around its latest occurrence (#6002), read only when opened. #}
+  <details style="font-size:0.8rem;margin-top:0.3rem;"
+           hx-get="/plugins/syslog/around?source={{ a.source_module|urlencode }}&amp;resource={{ a.resource_name|urlencode }}&amp;since={{ v.last_span.started_at.isoformat()|urlencode }}{% if v.last_span.ended_at %}&amp;until={{ v.last_span.ended_at.isoformat()|urlencode }}{% endif %}"
+           hx-trigger="toggle once" hx-target="find .anomaly-syslog" hx-swap="innerHTML">
+    <summary style="cursor:pointer;color:var(--text-muted);">Syslog around it</summary>
+    <div class="anomaly-syslog"><p class="field-hint" style="margin:0.3rem 0 0;">Reading…</p></div>
+  </details>
+  {%- endif %}
 </div>
 {%- endmacro %}

steward/templates/base.html

@@ -20,6 +20,7 @@
     <link rel="stylesheet" href="{{ url_for('static', filename='theme.css') }}">
     <link rel="stylesheet" href="{{ url_for('static', filename='steward.css') }}">
     <script src="{{ url_for('static', filename='chart-colors.js') }}"></script>
+    <script src="{{ url_for('static', filename='chart-marks.js') }}"></script>
     <script src="{{ url_for('static', filename='scroll-more.js') }}" defer></script>
     {# A form with data-confirm="…" asks in #confirm-dialog below before it submits (#5314). #}
     <script src="{{ url_for('static', filename='confirm.js') }}" defer></script>