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>

steward/templates/settings/_ansible_sources.html

@@ -26,7 +26,7 @@
             {% if src.type == 'git' %}
               {{ src.url or '(no URL)' }}
               <span style="color:var(--text-dim);margin-left:0.5rem;">branch: {{ src.branch or 'main' }}</span>
-              {% if src.pull_interval_seconds %}<span style="color:var(--text-dim);margin-left:0.5rem;">· pull every {{ src.pull_interval_seconds }}s</span>{% endif %}
+              {% if src.pull_interval_seconds %}<span style="color:var(--text-dim);margin-left:0.5rem;">· pulled every {{ src.pull_interval_seconds|duration }}</span>{% endif %}
             {% else %}
               {{ src.path or '(no path)' }}
             {% endif %}