feat(dashboard): merge top summary strip + Status widget into one Overview

Operator chose a single canonical summary. Repurpose the status_overview
widget into 'Overview' (host count + monitor up/down/pending + Alerts link;
key kept so existing dashboards upgrade in place) and remove the redundant
fixed top strip from the dashboard view. Drops _get_summary_stats and its
now-unused PingResult/DnsResult imports (rule 22).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/templates/dashboard/index.html

@@ -33,37 +33,8 @@
   </div>
 </div>
 
-{# ── Summary strip ─────────────────────────────────────────────────────────── #}
-<div style="display:grid;grid-template-columns:repeat(auto-fill,minmax(180px,1fr));gap:0.75rem;margin-bottom:1.5rem;">
-  <div class="card" style="margin-bottom:0;">
-    <div class="section-title" style="margin-bottom:0.5rem;">Hosts</div>
-    <span class="stat-val">{{ total_hosts }}</span>
-    <span class="stat-label">total</span>
-    <div style="margin-top:0.5rem;"><a href="/hosts/" style="font-size:0.8rem;">Manage →</a></div>
-  </div>
-  <div class="card" style="margin-bottom:0;">
-    <div class="section-title" style="margin-bottom:0.5rem;">Ping</div>
-    {% if ping_up + ping_down == 0 %}
-      <span style="color:var(--text-muted);font-size:0.85rem;">No hosts</span>
-    {% else %}
-      <span class="stat-val" style="color:var(--green);">{{ ping_up }}</span><span class="stat-label">up</span>
-      {% if ping_down %}&nbsp;<span class="stat-val" style="color:var(--red);">{{ ping_down }}</span><span class="stat-label">down</span>{% endif %}
-    {% endif %}
-  </div>
-  <div class="card" style="margin-bottom:0;">
-    <div class="section-title" style="margin-bottom:0.5rem;">DNS</div>
-    {% if dns_ok + dns_fail == 0 %}
-      <span style="color:var(--text-muted);font-size:0.85rem;">No hosts</span>
-    {% else %}
-      <span class="stat-val" style="color:var(--green);">{{ dns_ok }}</span><span class="stat-label">ok</span>
-      {% if dns_fail %}&nbsp;<span class="stat-val" style="color:var(--red);">{{ dns_fail }}</span><span class="stat-label">failed</span>{% endif %}
-    {% endif %}
-  </div>
-  <div class="card" style="margin-bottom:0;">
-    <div class="section-title" style="margin-bottom:0.5rem;">Alerts</div>
-    <a href="/alerts/" style="font-size:0.85rem;">View rules →</a>
-  </div>
-</div>
+{# The old fixed summary strip (Hosts/Ping/DNS/Alerts) was merged into the single
+   'Overview' widget (status_overview) so there's one canonical summary, not two. #}
 
 {# ── Widget grid (Gridstack; static until Edit is toggled) ──────────────────── #}
 {% if not widgets %}