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/status/widget.html

@@ -1,8 +1,16 @@
-{# status/widget.html — compact dashboard summary + problem list #}
-<div style="display:flex;gap:1.25rem;align-items:baseline;margin-bottom:0.6rem;">
+{# status/widget.html — the unified Overview: host count + monitor health
+   (up/down/pending) + alerts link + problem list. Replaced the old fixed
+   top summary strip. #}
+<div style="display:flex;flex-wrap:wrap;gap:1.25rem;align-items:baseline;margin-bottom:0.6rem;">
+  <span>
+    {% if session.user_id %}<a href="/hosts/" style="color:inherit;text-decoration:none;">{% endif %}
+    <span class="stat-val" style="font-size:1.5rem;">{{ total_hosts }}</span><span class="stat-label">host{{ '' if total_hosts == 1 else 's' }}</span>
+    {% if session.user_id %}</a>{% endif %}
+  </span>
   <span><span class="stat-val" style="font-size:1.5rem;color:var(--green);">{{ up }}</span><span class="stat-label">up</span></span>
   <span><span class="stat-val" style="font-size:1.5rem;color:{% if down %}var(--red){% else %}var(--text-dim){% endif %};">{{ down }}</span><span class="stat-label">down</span></span>
   <span><span class="stat-val" style="font-size:1.5rem;color:{% if pending %}var(--yellow){% else %}var(--text-dim){% endif %};">{{ pending }}</span><span class="stat-label">pending</span></span>
+  {% if session.user_id %}<a href="/alerts/" style="margin-left:auto;align-self:center;font-size:0.8rem;">Alerts →</a>{% endif %}
 </div>
 
 {% set problems = entries | rejectattr("status", "equalto", "up") | list %}