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>

plugins/docker/service.py

@@ -183,3 +183,16 @@ async def recent_failures_by_container(db, since) -> dict[tuple[str, str], list]
     for e in rows:
         out.setdefault((e.host_id, e.container_name), []).append(e)
     return out
+
+
+PRUNE_TARGETS = ("containers", "images", "system")
+
+
+def prune_extra_vars(prune_target: str) -> dict:
+    """Extra-vars for the bundled docker_prune playbook. "Prune unused images"
+    means ALL unused (docker image prune -a), not just dangling; the full system
+    prune stays conservative (-f, no -a) per the operator's choice (m78)."""
+    extra_vars: dict = {"prune_target": prune_target}
+    if prune_target == "images":
+        extra_vars["prune_all_images"] = True
+    return extra_vars