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/docker/routes.py

@@ -529,6 +529,11 @@ async def swarm():
     return await render_template("docker/swarm.html", swarms=swarms)
 
 
+# How many images a host agent reports, largest first (host_agent agent.py
+# _disk_images caps its list here); a list this long may be missing smaller ones.
+IMAGES_REPORTED = 50
+
+
 @docker_bp.get("/disk")
 @require_role(UserRole.viewer)
 async def disk():
@@ -569,7 +574,8 @@ async def disk():
     images_by_host: dict[str, list] = {}
     for im in images:
         images_by_host.setdefault(im.host_id, []).append({
-            "repo_tag": im.repo_tag, "size": human_bytes(im.size),
+            "repo_tag": None if im.repo_tag in ("<none>", "", None) else im.repo_tag,
+            "image_id": im.image_id, "size": human_bytes(im.size),
             "shared": human_bytes(im.shared_size), "containers": im.containers,
             "reclaimable": im.containers == 0,
         })
@@ -578,6 +584,7 @@ async def disk():
         {
             "host_id": s.host_id,
             "host_name": hosts[s.host_id].name if s.host_id in hosts else s.host_id,
+            "as_of": s.updated_at,
             "summary": {
                 "images_total": s.images_total, "images_active": s.images_active,
                 "images_size": human_bytes(s.images_size),
@@ -591,6 +598,8 @@ async def disk():
             },
             "stopped": stopped_by_host.get(s.host_id, 0),
             "images": images_by_host.get(s.host_id, []),
+            # The agent reports the largest IMAGES_REPORTED images (agent._disk_images).
+            "images_capped": len(images_by_host.get(s.host_id, [])) >= IMAGES_REPORTED,
             "has_target": s.host_id in target_by_host,
         }
         for s in summaries