feat(ui): Disk, Traefik, UniFi and Settings say things plainly (#5212)

#5212 "Plain labels: no raw ids, scopes, metric keys or unexplained jargon",
batch 3:

- Disk page: each tile says what it holds. "Writable layers" becomes
  "Container files" and Build cache says it is safe to clear. Shared is
  "Shared with other images" with a tooltip, and "dangling" is gone.
  Untagged images show by id instead of "<none>", a capped list says
  "The 50 largest of N images", and each host shows "as of" its report.
- Traefik: an expired certificate reads "expired 12 days ago", not "-12
  days" (cert_left). The Traffic empty state knows whether the access log
  is on: off points to Settings → Plugins → Traefik; on says to check the
  mounted log path.
- Moments use |ago with an exact UTC tooltip: UniFi last seen, alarms,
  events, speed test and DPI; AI token last used.
- Settings: the Auth tab is "Authentication" like its breadcrumb, plugin
  fields read "Metrics URL" not metrics_url (field_label), a source's pull
  interval is "every 1h", and the last report time drops the ISO "T".

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

plugins/unifi/templates/unifi/security.html

@@ -21,7 +21,7 @@
           </div>
           <div>{{ al.message }}</div>
           <div style="color:var(--text-dim);font-size:0.75rem;margin-top:0.1rem;">
-            {{ al.alarm_time.strftime("%Y-%m-%d %H:%M") }} UTC
+            {{ al.alarm_time|ago }}
           </div>
         </td>
       </tr>
@@ -45,7 +45,7 @@
           <div style="color:var(--text-dim);font-size:0.8rem;">{{ al.message }}</div>
         </td>
         <td style="padding:0.25rem 0;text-align:right;color:var(--text-dim);font-size:0.75rem;white-space:nowrap;">
-          {{ al.alarm_time.strftime("%m-%d %H:%M") }}
+          {{ al.alarm_time|ago }}
         </td>
       </tr>
       {% endfor %}