fix(ansible): overlapping runs: one per host, one per schedule, one action run per alert rule (#5158)

- One run per host: start_run claims every host it touches (addresses read
  from the inventory Steward wrote; a source's own inventory file is claimed
  as that file) before it takes a run slot. The claim is all-or-nothing. A run
  waiting on a host shows queued and names the run it waits for, honours a
  cancel, and fails after HOST_WAIT_SECONDS (1 h) with which host and run.
- A due schedule whose previous run is still queued or running skips the
  firing: last_run_at moves on, last_run_id still names the run going, and
  last_error says "Skipped: the previous run was still going". The Schedules
  page shows that beside the run (muted), and a launch error in red.
- An alert rule that fires while the action run from an earlier firing is
  still going starts no new run; the event says so and names the run. An
  in-process set closes the gap between the check and the run being linked.
- docs/core/ansible.md: queued/cancelled statuses and the overlap rules.

Tests: tests/core/test_ansible_overlap.py (claim keys, waiting, all-or-nothing,
cancel, deadline) and tests/integration/test_ansible_overlap.py (two real
runs on one host take turns; schedule skip then fire; alert action skip then
start).

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

steward/templates/ansible/schedules.html

@@ -38,13 +38,18 @@
     <td style="font-size:0.85rem;" title="{{ s.inventory_scope }}">{{ row.scope_label }}</td>
     <td style="font-size:0.85rem;">{{ fmt_interval(s.interval_seconds) }}</td>
     <td style="font-size:0.82rem;">
-      {% if s.last_error %}
-        <span style="color:var(--red);" title="{{ s.last_error }}">launch error</span>
-      {% elif row.last_run %}
+      {% if row.last_run %}
         {% set sc = {"queued":"var(--text-dim)","running":"var(--yellow)","success":"var(--green)","failed":"var(--red)","interrupted":"var(--orange)","cancelled":"var(--orange)"}.get(row.last_run.status.value, "var(--text-muted)") %}
         <a href="/ansible/runs/{{ row.last_run.id }}" style="color:{{ sc }};font-weight:500;">{{ row.last_run.status.value }}</a>
-        <span style="color:var(--text-dim);">· {{ s.last_run_at.strftime("%m-%d %H:%M") }}</span>
-      {% else %}
+        <span style="color:var(--text-dim);">· {{ row.last_run.started_at.strftime("%m-%d %H:%M") }}</span>
+      {% endif %}
+      {% if s.last_error %}
+        {# With a run beside it, the last firing was skipped because that run was
+           still going (#5158); without one, the firing couldn't start a run. #}
+        <div style="color:{{ 'var(--text-muted)' if row.last_run else 'var(--red)' }};">
+          {{ s.last_error }} · {{ s.last_run_at.strftime("%m-%d %H:%M") }}
+        </div>
+      {% elif not row.last_run %}
         <span style="color:var(--text-dim);">never</span>
       {% endif %}
     </td>