feat(dashboard): a curated default layout, merged duplicate widgets, a labelled Overview (#5213)

- New installs start from widgets.RECOMMENDED, packed row by row for the
  enabled plugins; the edit drawer can reset a dashboard to it.
- Host Agent — Resources folds into Hosts — Overview (which gains load 1m),
  UniFi — Devices into UniFi — Overview; migration 0032 moves existing
  dashboards onto the survivors.
- The Overview labels what it counts (hosts, monitors up/down/pending,
  alerts firing) and lists firing alerts and down monitors with since-times.
- Uptime polls every 5 minutes (poll_seconds) instead of every cycle.

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

steward/templates/dashboard/_widget_drawer.html

@@ -5,7 +5,14 @@
   <div style="display:flex;justify-content:space-between;align-items:center;margin-bottom:0.75rem;
               position:sticky;top:0;background:var(--bg-card);padding-bottom:0.5rem;">
     <div class="section-title" style="margin-bottom:0;">Add a widget</div>
-    <button type="button" class="btn btn-sm" id="dash-edit-done">Done</button>
+    <span style="display:flex;gap:0.5rem;align-items:center;">
+      <form method="post" action="/d/{{ dashboard.id }}/edit/reset" style="margin:0;"
+            data-confirm="Replace every widget on this dashboard with the recommended layout? Widgets you added or renamed are removed.">{{ csrf_field() }}
+        <button type="submit" class="btn btn-ghost btn-sm"
+                title="Overview first, then hosts and monitors, then each integration">Reset to the recommended layout</button>
+      </form>
+      <button type="button" class="btn btn-sm" id="dash-edit-done">Done</button>
+    </span>
   </div>
   {% if addable %}
   {% set _groups = [("core", "Core monitors"), ("capability", "Monitoring capabilities"), ("integration", "Integrations")] %}