feat(timeline): record a change by hand from the Timeline, a host's page or MCP log_change (#6350)

A change Steward can't see happen (a config edited, a disk swapped) is
recorded by whoever made it: what was done, its area, when (in the reader's
own zone), the hosts, what it was done to and a detail. Its author or an
admin edits or deletes it; recording, editing and deleting are audited and
those audit rows stay off the timeline. log_change records one as
"<user> via MCP", editable by the token's user.

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

steward/timeline/catalog.py

@@ -75,6 +75,8 @@ for _t in (
      "What an alert rule watches stopped reporting."),
     ("alert.resumed", "Readings resumed", "alert", "monitoring", True,
      "What an alert rule watches reported again after a silence."),
+    ("change.recorded", "Change recorded", "change", "service", True,
+     "A change someone recorded by hand, on the Timeline or a host's page, or through MCP."),
     ("ansible.changed", "Playbook changed something", "automation", "host_os", True,
      "A playbook run finished and changed at least one host."),
     ("ansible.unchanged", "Playbook changed nothing", "automation", "host_os", False,
@@ -145,6 +147,8 @@ _AUDIT_TYPES = (
     ("account.time_zone", None), ("account.email", None),
     ("host_agent.maintenance_plan", "steward.config"), ("host_agent.maintenance", None),
     ("docker.prune.", None),
+    # A change recorded by hand is on the timeline as itself (timeline.changes).
+    ("timeline.change", None),
     ("auth.login", "steward.signin"), ("auth.setup", "steward.config"),
     ("account.", "steward.access"), ("user.", "steward.access"), ("api_token.", "steward.access"),
     ("backup.", "steward.backup"),