feat(docker): container log viewer + Settings controls [M79 step 5]

The user-facing half (rule 27). Per-container log viewer + admin controls, so
container logs are something the operator can actually touch.

Viewer (plugins/docker):
- /container/<host>/<name>/logs full page + /logs/lines HTMX fragment polled
  every 5s (near-live follow); stream filter (all/stdout/stderr) + case-insensitive
  text search; newest-first so the latest lines survive the poll's scroll reset;
  empty/loading states; a "View logs" link from the container detail page.
  Jinja auto-escapes log content (no markup injection).

Settings (Thresholds & Retention tab):
- global on/off toggle, comma-separated exclude list, retention days + max MB
  per container — DB-backed, no restart. The toggle + exclude are enforced
  authoritatively at ingest (_persist_logs drops disabled/excluded lines), since
  the push model has no channel to tell an agent to stop.

Tests: route-defined smoke; template-parse covers the new templates; integration
test for the ingest-time toggle + exclude enforcement.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CAGR73DUowdVFVvYzLXC5C

plugins/docker/templates/docker/container_detail.html

@@ -26,6 +26,7 @@
 <div style="font-size:0.82rem;color:var(--text-muted);margin-bottom:1.5rem;">
   {{ container.status }}{% if uptime %} · up {{ uptime }}{% endif %}
   {% if host %} · on <a href="/hosts/{{ host.id }}" style="color:var(--text-muted);">{{ host.name }}</a>{% endif %}
+  · <a href="/plugins/docker/container/{{ host_id }}/{{ name }}/logs">View logs</a>
 </div>
 
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