feat(docker): swarm topology view + image/disk usage page (milestone 77 #942)

Two new read-only sub-pages, linked from the Docker index header only when the
data exists (non-swarm / Docker-less installs aren't offered empty pages):

- /plugins/docker/swarm — services with replica health (running/desired,
  colour-coded green/amber/red), Swarm nodes (role/availability/status, leader
  badge), and task→node placement with node ids resolved to hostnames. Grouped
  by reporting manager host. Empty state explains manager-only collection.

- /plugins/docker/disk — per-host reclaimable space, image/layer/container/
  volume/build-cache sizes, stopped-container count, and a per-image table
  (size, shared, ref count, reclaimable badge). Notes prune actions are deferred.

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

plugins/docker/templates/docker/swarm.html

@@ -0,0 +1,86 @@
+{# docker/swarm.html — Swarm topology: services, replica health, nodes, placement #}
+{% extends "base.html" %}
+{% block title %}Swarm — Docker — Steward{% 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 %}
+{% for g in host_groups %}
+<div style="margin-bottom:2rem;">
+  <div style="display:flex;align-items:baseline;gap:0.6rem;margin-bottom:0.75rem;">
+    <span style="font-weight:600;font-size:0.95rem;">{{ g.host_name }}</span>
+    <span style="font-size:0.78rem;color:var(--text-muted);">manager view</span>
+  </div>
+
+  {# ── Services ─────────────────────────────────────────────────────────── #}
+  <div class="card-flush" style="margin-bottom:1rem;">
+    <table class="table">
+      <thead>
+        <tr>
+          <th>Service</th><th>Mode</th><th>Replicas</th><th>Image</th><th>Placement</th>
+        </tr>
+      </thead>
+      <tbody>
+        {% for s in g.services %}
+        <tr>
+          <td style="font-weight:500;font-size:0.9rem;">{{ s.name }}</td>
+          <td style="font-size:0.82rem;color:var(--text-muted);">{{ s.mode }}</td>
+          <td style="font-family:ui-monospace,monospace;font-size:0.88rem;">
+            <span style="color:{% if s.healthy %}var(--green){% elif s.down %}var(--red){% elif s.degraded %}var(--orange){% else %}var(--text-muted){% endif %};">
+              {{ s.running }}/{{ s.desired }}
+            </span>
+          </td>
+          <td style="font-size:0.8rem;color:var(--text-muted);max-width:220px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;">{{ s.image or "—" }}</td>
+          <td style="font-size:0.78rem;color:var(--text-muted);">
+            {% for p in s.placement %}{{ p.node }} ({{ p.running }}){% if not loop.last %}, {% endif %}{% else %}—{% endfor %}
+          </td>
+        </tr>
+        {% else %}
+        <tr><td colspan="5" style="color:var(--text-muted);font-size:0.85rem;text-align:center;padding:1.5rem;">No services on this manager.</td></tr>
+        {% endfor %}
+      </tbody>
+    </table>
+  </div>
+
+  {# ── Nodes ────────────────────────────────────────────────────────────── #}
+  <div class="card-flush">
+    <table class="table">
+      <thead>
+        <tr><th>Node</th><th>Role</th><th>Availability</th><th>Status</th></tr>
+      </thead>
+      <tbody>
+        {% for n in g.nodes %}
+        <tr>
+          <td style="font-weight:500;font-size:0.9rem;">
+            {{ n.hostname or n.node_id }}
+            {% if n.leader %}<span title="cluster leader" style="font-size:0.68rem;color:var(--accent);border:1px solid var(--accent);border-radius:3px;padding:0 0.3rem;margin-left:0.3rem;">leader</span>{% endif %}
+          </td>
+          <td style="font-size:0.82rem;color:var(--text-muted);">{{ n.role }}</td>
+          <td style="font-size:0.82rem;color:{% if n.availability == 'active' %}var(--text){% else %}var(--orange){% endif %};">{{ n.availability }}</td>
+          <td style="font-size:0.82rem;">
+            <span class="dot {% if n.status == 'ready' %}dot-up{% else %}dot-down{% endif %}"></span>
+            <span style="color:{% if n.status == 'ready' %}var(--green){% else %}var(--red){% endif %};">{{ n.status }}</span>
+          </td>
+        </tr>
+        {% else %}
+        <tr><td colspan="4" style="color:var(--text-muted);font-size:0.85rem;text-align:center;padding:1.5rem;">No nodes reported.</td></tr>
+        {% endfor %}
+      </tbody>
+    </table>
+  </div>
+</div>
+{% endfor %}
+{% else %}
+<div class="card" style="text-align:center;padding:3rem;">
+  <div style="color:var(--text-muted);font-size:0.9rem;">
+    No Swarm topology reported. A Steward host agent running on a Swarm
+    <strong>manager</strong> reports services, nodes, and task placement here —
+    workers and non-swarm hosts contribute only their local containers.
+  </div>
+</div>
+{% endif %}
+{% endblock %}