feat(hosts): the live strip shows the hottest sensor's temperature, get_host marks sensors that don't count, and the Monitors card's button reads "Add" (#6803)

- The host page's live strip gains a Temperature tile: temp_c_max (real
  thermometers only), its last 6 h and the sensor setting it, graded by
  Settings → Thresholds and counted in the header's worst reading, in °C.
- MCP get_host: each temperature carries `counted`; an unwired input is
  `counted: false` with `not_counted_because`, listed after the real ones.
  host_agent registers the judge (judge_sensors), so core imports no plugin.
- The Monitors card's "Add monitor" wrapped into two lines beside the
  uptime; it reads "Add", titled "Add a monitor for this host".

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

steward/templates/hosts/detail.html

@@ -61,7 +61,7 @@
   <div style="display:flex;align-items:baseline;justify-content:space-between;margin-bottom:0.5rem;">
     <h3 class="section-title" style="margin-bottom:0;">Monitors</h3>
     {% if session.user_role in ['operator', 'admin'] %}
-    <a href="/monitors/new?host_id={{ host.id }}" class="btn btn-ghost btn-sm" style="margin-left:auto;margin-right:0.75rem;">Add monitor</a>
+    <a href="/monitors/new?host_id={{ host.id }}" class="btn btn-ghost btn-sm" style="margin-left:auto;margin-right:0.75rem;flex-shrink:0;" title="Add a monitor for this host">Add</a>
     {% endif %}
     {% if uptime %}
     <span style="font-size:0.8rem;color:var(--text-muted);">