fix(docker): dedup widget counts across swarm managers; show failures not stopped

The running count was inflated: swarm-aware agents on every manager list
cluster-wide tasks, so the same container (identical container_id) was reported
once per manager and the dashboard widgets summed them. The earlier swarm dedup
only covered the Swarm topology page — the widgets read raw rows.

- _dedup_by_container_id(): collapse rows sharing a non-empty container_id
  (globally unique, so only true duplicates merge); first occurrence wins under
  the running-first ordering. Applied in both the containers and resources
  widgets before counting/limiting. Rows without a container_id (older agents)
  are kept as-is.
- Replaced the static "stopped" tally — not actionable — with "failed (24h)":
  distinct containers with a die/oom event in the last 24h (DISTINCT so the
  managers' duplicate events don't double it), rendered red when non-zero.
- widget.html empty-state now keys off total_count.
- Regression test: same container_id from two managers counts once; id-less rows
  all kept.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016Jg27rgypiW2efULXJDtMC

plugins/docker/templates/docker/widget.html

@@ -1,19 +1,17 @@
 {# docker/widget.html — dashboard widget: container status overview, by host #}
-{% if running_count == 0 and stopped_count == 0 %}
+{% if total_count == 0 %}
 <p class="empty" style="padding:0.5rem 0;font-size:0.85rem;">No containers reported yet.</p>
 {% else %}
 
-<div style="display:flex;gap:1rem;margin-bottom:0.65rem;">
+<div style="display:flex;gap:1.25rem;margin-bottom:0.65rem;">
   <div>
     <span style="font-size:1.4rem;font-weight:700;line-height:1;color:var(--green);">{{ running_count }}</span>
     <span style="font-size:0.78rem;color:var(--text-muted);margin-left:0.25rem;">running</span>
   </div>
-  {% if stopped_count %}
-  <div>
-    <span style="font-size:1.4rem;font-weight:700;line-height:1;color:var(--text-muted);">{{ stopped_count }}</span>
-    <span style="font-size:0.78rem;color:var(--text-muted);margin-left:0.25rem;">stopped</span>
+  <div title="Distinct containers with a die or OOM event in the last 24h">
+    <span style="font-size:1.4rem;font-weight:700;line-height:1;color:{% if failed_24h %}var(--red){% else %}var(--text-muted){% endif %};">{{ failed_24h }}</span>
+    <span style="font-size:0.78rem;color:var(--text-muted);margin-left:0.25rem;">failed (24h)</span>
   </div>
-  {% endif %}
 </div>
 
 {% for g in host_groups %}