refactor: remove broken NUT/UPS plugin and managed-NUT startup

The UPS plugin's default driver was snmp-ups, so NUT was just translating
network SNMP back into its own protocol — no value over polling the UPS
directly through the existing snmp plugin. The managed-NUT entrypoint path
also broke container startup when config was incomplete.

Deletes nut_setup.py, the NUT block from entrypoint.sh, NUT packages from
the Dockerfile, the ups entry from the plugin catalog example, and the
ups wiring in alerts METRIC_CATALOG, widgets, settings routes, and the
rules form. The plugins/ups source tree (untracked) is also removed from
the working copy. Existing ups_* DB tables are orphaned but harmless in
dev; a drop migration isn't needed.

Follow-up: rebuild "on battery → Ansible shutdown" automation on top of
the alerts system as a new action type that runs a playbook.

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

roundtable/settings/routes.py

@@ -404,11 +404,6 @@ def _build_plugin_cfg_from_form(plugin: dict, form) -> dict:
                     plugin_cfg[cfg_key] = default_val
             else:
                 plugin_cfg[cfg_key] = raw_val
-    # Managed NUT: when nut_managed is on, the NUT daemon runs in this container
-    # — force nut_host/port to localhost so the plugin connects automatically.
-    if name == "ups" and plugin_cfg.get("nut_managed"):
-        plugin_cfg["nut_host"] = "localhost"
-        plugin_cfg["nut_port"] = 3493
     return plugin_cfg
 
 
@@ -483,9 +478,6 @@ async def save_plugin_detail(name: str):
         from roundtable.core.plugin_manager import hot_reload_plugin
         hot_reload_plugin(current_app._get_current_object(), name)
 
-    if name == "ups":
-        _sync_nut_managed_config(form)
-
     return redirect(url_for("settings.plugin_detail", name=name))
 
 
@@ -546,35 +538,6 @@ async def plugin_repos_save(idx: int):
     return await _plugin_repos_partial({"plugins.repositories": repos})
 
 
-def _sync_nut_managed_config(form) -> None:
-    """Write or remove /data/nut_managed.json based on UPS plugin managed NUT settings."""
-    import json
-    nut_managed_path = Path("/data/nut_managed.json")
-    nut_managed = "plugin.ups.nut_managed" in form
-    ups_host = form.get("plugin.ups.nut_ups_host", "").strip()
-    # Only write the file when managed mode is on AND a host is configured.
-    # Without a host, NUT can't start and the container would loop on errors.
-    if nut_managed and ups_host:
-        cfg = {
-            "ups_host":       ups_host,
-            "driver":         form.get("plugin.ups.nut_driver", "snmp-ups").strip(),
-            "ups_name":       form.get("plugin.ups.ups_name", "ups").strip(),
-            "snmp_community": form.get("plugin.ups.nut_snmp_community", "public").strip(),
-            "snmp_version":   form.get("plugin.ups.nut_snmp_version", "v1").strip(),
-            "username":       form.get("plugin.ups.nut_username", "").strip(),
-            "password":       form.get("plugin.ups.nut_password", "").strip(),
-        }
-        try:
-            nut_managed_path.write_text(json.dumps(cfg, indent=2))
-        except OSError as exc:
-            logger.warning("Could not write %s: %s", nut_managed_path, exc)
-    else:
-        try:
-            nut_managed_path.unlink(missing_ok=True)
-        except OSError as exc:
-            logger.warning("Could not remove %s: %s", nut_managed_path, exc)
-
-
 # ── Plugin catalog (HTMX partial) ─────────────────────────────────────────────
 
 @settings_bp.get("/plugins/catalog/")