fix(ui): a reading's age no longer puts a <time> element inside a title attribute (#5467)

The `when` filter returns a <time> element, so title="{{ at|when }}" wrote raw
markup into the attribute. That broke the hover text, and in the rule form's
metric preview (#5475) it leaked a stray `">` into the page. `ago` already
carries the exact time as its own tooltip, so both places drop the title.
Also fixes #5467's page test, which needed the escaped apostrophe.

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

steward/templates/settings/system.html

@@ -24,7 +24,7 @@
         <td class="cell-name"><span title="{{ metric_label(r.metric) }}">{{ metric_label(r.metric) }}</span>
           <div class="cell-sub" title="{{ metric_about(r.metric) }}">{{ metric_about(r.metric) }}</div></td>
         <td class="nowrap">{{ metric_value(r.metric, r.now) }}
-          {%- if r.at %}<div class="cell-sub" title="{{ r.at|when }}">{{ r.at|ago }}</div>{% endif %}</td>
+          {%- if r.at %}<div class="cell-sub">{{ r.at|ago }}</div>{% endif %}</td>
         <td class="nowrap">
           {%- if r.low is not none %}{{ metric_value(r.metric, r.low) }} – {{ metric_value(r.metric, r.high) }}
           <span class="metric-preview-spark" aria-hidden="true">{{ r.spark|safe }}</span>