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/ansible/runner.py

@@ -16,6 +16,19 @@ from steward.ansible.inventory_gen import (
 )
 from steward.models.ansible import AnsibleRun, AnsibleRunStatus
 
+# A run in one of these hasn't finished: a schedule or an alert action whose
+# previous run is still in one skips its next firing (#5158).
+IN_FLIGHT = (AnsibleRunStatus.queued, AnsibleRunStatus.running)
+
+
+async def run_in_flight(db, run_id: str | None) -> bool:
+    """Whether run_id names a run that hasn't finished. Runs left running by a
+    restart are marked interrupted at startup, so this can't stick."""
+    if not run_id:
+        return False
+    run = await db.get(AnsibleRun, run_id)
+    return run is not None and run.status in IN_FLIGHT
+
 
 async def trigger_run(
     app,