feat: managed NUT setup, plugin config improvements, migration fix

- Add managed NUT mode: configure NUT daemon from Settings → Plugins
  (UPS plugin), writes /data/nut_managed.json read by entrypoint on
  restart — no env vars or USB passthrough required
- entrypoint.sh: start NUT from /data/nut_managed.json or NUT_MANAGED=1
  env var; drop to app user via gosu after NUT daemons start
- nut_setup.py: support --from-file <json> in addition to env vars
- Dockerfile: add nut, nut-client, gosu packages and entrypoint
- docker-compose.yml: document optional NUT_MANAGED env var block
- Fix plugin hot-reload migration failure: pass all plugin migration
  dirs to Alembic so previously-stamped revisions from other plugins
  remain resolvable (fixes UPS and any plugin with depends_on)
- Fix plugin list-type config (e.g. SNMP devices) rendering as broken
  text input — now shows a read-only note to edit plugin.yaml instead
- Fix _sync_nut_managed_config: only write JSON when nut_ups_host is
  non-empty, preventing NUT startup loop on container restart

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fabledscryer/templates/settings/plugins.html

@@ -68,7 +68,17 @@
 
       {% for cfg_key, cfg_default in plugin.config.items() %}
 
-        {% if cfg_default is mapping %}
+        {% if cfg_default is iterable and cfg_default is not string and cfg_default is not mapping %}
+          {# List — cannot be edited via a flat form; must be set in plugin.yaml #}
+          <div style="display:flex;align-items:flex-start;gap:0.5rem;padding:0.5rem 0.75rem;
+                      background:var(--bg);border-radius:5px;border:1px solid var(--border);
+                      font-size:0.82rem;color:var(--text-muted);">
+            <span style="flex-shrink:0;">📋</span>
+            <span><strong style="color:var(--text);">{{ cfg_key }}</strong> — list config, edit in
+              <code>plugin.yaml</code> ({{ cfg_default | length }} item{{ 's' if cfg_default | length != 1 }}).</span>
+          </div>
+
+        {% elif cfg_default is mapping %}
           {# Nested dict group #}
           <div style="padding:0.6rem 0.75rem;background:var(--bg);border-radius:5px;border:1px solid var(--border);">
             <div style="font-size:0.75rem;color:var(--text-muted);text-transform:uppercase;letter-spacing:0.05em;margin-bottom:0.6rem;">{{ cfg_key }}</div>