feat(mcp): automation tools — playbooks, runs, schedules, alert actions, docker prune

MCP-6 #4970 "Automation tools: playbooks, runs, schedules, alert actions".

Viewer: list_playbooks, get_playbook (secret defaults masked), list_inventory
(variable names only), list_ansible_runs, get_ansible_run (log tail + grep),
list_schedules, wait_for_run (polls, 120s cap).

Operator: run_playbook (check mode unless check=false; a steward:confirm
playbook applies only with confirmed=true; secret variables reach the run
but are never stored, audited or returned), cancel_ansible_run, and
create/update/delete_schedule (secrets refused, check by default).

Admin: set_alert_action, and the docker plugin's prune_docker, which
previews from the disk report unless check=false (Ansible's check mode
skips the prune commands, so a check run would show nothing).

Every write is audited as "<user> via MCP" with the token id; the audit
tool's user filter includes those rows. prune_extra_vars moves to the
docker service so the page and the tool share it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/plugins/docker/test_mcp_tools.py

@@ -1,8 +1,11 @@
 """The docker plugin's MCP tools: what counts as a problem, and how it is reported."""
+import inspect
 from datetime import datetime, timedelta, timezone
 from types import SimpleNamespace as NS
 from unittest.mock import MagicMock
 
+import pytest
+
 import plugins.docker as docker_plugin
 from plugins.docker import mcp_tools as t
 
@@ -78,3 +81,21 @@ def test_plugin_exposes_the_mcp_hooks():
     for call in reg.call_args_list:
         assert call.kwargs["read_only"] is True
     assert callable(docker_plugin.mcp_overview)
+
+
+def test_prune_preview_sizes_what_each_target_removes():
+    usage = NS(images_reclaimable=3000, build_cache_size=70)
+    assert t.prune_preview("containers", usage, 4) == {"stopped_containers": 4}
+    assert t.prune_preview("images", usage, 4) == {"unused_images_bytes": 3000}
+    system = t.prune_preview("system", usage, 4)
+    assert system["stopped_containers"] == 4 and system["build_cache_bytes"] == 70
+    assert t.prune_preview("images", None, 0) == {"unused_images_bytes": None}
+
+
+async def test_prune_docker_refuses_an_unknown_target_before_reading_anything(monkeypatch):
+    def _no_db():
+        raise AssertionError("touched the database")
+    monkeypatch.setattr(t, "db_session", _no_db)
+    with pytest.raises(ValueError, match="'volumes' is not one of containers, images, system"):
+        await t.prune_docker("nas", "volumes")
+    assert inspect.signature(t.prune_docker).parameters["check"].default is True