Add datetime to the search results

I find it helpful (especially when going through a long list of
results) to know how far back in time I'm looking.

A note on the timestamp being used: it's the search index
timestamp. Using the card or comment `updated_at` is fraught because
we do so much touching of records (e.g., comment is touched when a
reaction is added; card is touched when a comment is added). Let's
display the search record's `created_at`, which is the ordering used
for the overall results.

app/views/searches/_result.html.erb

@@ -15,7 +15,7 @@
       <% end %>
     </div>
     <div class="overflow-ellipsis translucent txt-ink">
-      <%= result.card.board.name %>
+      <%= result.card.board.name %> · <%= local_datetime_tag(result.created_at, style: :timeordate) %>
     </div>
   <% end %>
 </li>