feat(widgets): Routers and Hosts problem rows say since when (#5810)

Routers: a router in trouble reads 'started 2h ago' or 'all of the last
24 h', from problem_since over the day's history, read for the troubled
routers only (a certificate's problem carries its own date). Hosts: a
down host reads 'a monitor is down for 3h'; host_glance keeps the
down_since host_status already had.

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

steward/templates/hosts/overview_widget.html

@@ -27,7 +27,7 @@
     <td class="w-name" title="{{ r.host.name }}">
       {{- status_dot(r.state) -}}
       {% if session.user_id %}<a href="/hosts/{{ r.host.id }}">{{ r.host.name }}</a>{% else %}{{ r.host.name }}{% endif %}
-      {%- if r.state == 'down' %}<span class="w-sub tone-crit">a monitor is down</span>
+      {%- if r.state == 'down' %}<span class="w-sub tone-crit">a monitor is down{% if r.down_since %} for {{ r.down_since|ago|replace(' ago', '') }}{% endif %}</span>
       {%- elif r.state == 'stale' %}<span class="w-sub tone-warn">agent last reported {{ a.last_at|ago }}; figures are from then</span>
       {%- elif not a %}<span class="w-sub">no agent</span>{% endif %}
     </td>