fix(ui): unify header/breadcrumb treatment, drop redundant back buttons

The page-top chrome was inconsistent: most nested views used the breadcrumb
kicker + page-title pattern, but plugin sub-pages used ad-hoc "← back" links,
~11 pages stacked a breadcrumb AND a redundant ancestor back button, and two
(monitors/edit, hosts/uptime) had a back button but no breadcrumb. The
settings/plugin_detail page stacked all of it at once.

Unify on the breadcrumb-led model:
- settings/_tabs.html: drop the hardcoded "Settings" h1; the breadcrumb
  ("Settings › …") plus the tab strip is the header.
- settings/plugin_detail: drop the "← Plugins" back button.
- docker container_detail/swarm/disk + snmp/device: replace ad-hoc back links
  with the standard crumbs() breadcrumb.
- host_agent, ansible/*, alerts/maintenance: remove redundant ancestor back
  buttons (the breadcrumb's parent crumbs already link there); keep lateral
  shortcuts (Inventory/Schedules/Browse/Targets/Groups/New).
- monitors/edit, hosts/uptime: add the missing breadcrumb, drop the back link.

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

plugins/docker/templates/docker/container_detail.html

@@ -1,12 +1,10 @@
 {# docker/container_detail.html — full detail page for one container #}
 {% extends "base.html" %}
+{% from "_macros.html" import crumbs %}
 {% block title %}{{ name }} — Docker — Steward{% endblock %}
+{% block breadcrumb %}{{ crumbs([("Docker", "/plugins/docker/"), (name, "")]) }}{% endblock %}
 {% block content %}
 
-<div style="margin-bottom:1rem;">
-  <a href="/plugins/docker/" style="font-size:0.82rem;color:var(--text-muted);text-decoration:none;">← All containers</a>
-</div>
-
 {% if container is none %}
 <div class="card" style="text-align:center;padding:3rem;">
   <div style="font-weight:600;margin-bottom:0.4rem;">Container not found</div>

plugins/docker/templates/docker/disk.html

@@ -1,11 +1,10 @@
 {# docker/disk.html — image/disk usage: reclaimable space, per-image sizes #}
 {% extends "base.html" %}
+{% from "_macros.html" import crumbs %}
 {% block title %}Disk — Docker — Steward{% endblock %}
+{% block breadcrumb %}{{ crumbs([("Docker", "/plugins/docker/"), ("Image & disk usage", "")]) }}{% endblock %}
 {% block content %}
 
-<div style="margin-bottom:1rem;">
-  <a href="/plugins/docker/" style="font-size:0.82rem;color:var(--text-muted);text-decoration:none;">← All containers</a>
-</div>
 <h1 class="page-title" style="margin-bottom:0.4rem;">Image &amp; disk usage</h1>
 <p style="font-size:0.82rem;color:var(--text-muted);margin-bottom:1.5rem;">
   Reclaimable = space held by images no container references. Cleanup actions

plugins/docker/templates/docker/swarm.html

@@ -1,11 +1,10 @@
 {# docker/swarm.html — Swarm topology: services, replica health, nodes, placement #}
 {% extends "base.html" %}
+{% from "_macros.html" import crumbs %}
 {% block title %}Swarm — Docker — Steward{% endblock %}
+{% block breadcrumb %}{{ crumbs([("Docker", "/plugins/docker/"), ("Swarm", "")]) }}{% endblock %}
 {% block content %}
 
-<div style="margin-bottom:1rem;">
-  <a href="/plugins/docker/" style="font-size:0.82rem;color:var(--text-muted);text-decoration:none;">← All containers</a>
-</div>
 <h1 class="page-title" style="margin-bottom:1.5rem;">Swarm</h1>
 
 {% if host_groups %}