feat(monitors): a DNS monitor can name a resolver; the host page puts Ansible above Docker (#5214)

DNS monitors take an optional Resolver, a server's IP. Set, the check asks
that server directly for A and AAAA over UDP and records how long it took
to answer; empty keeps today's lookup through the container's resolver.
"Does my local DNS still answer for public names" and "does 1.1.1.1" are
now separate monitors. No new dependency.

On a host's page the Ansible card moves above the Docker list, which can
run to dozens of containers and hid it.

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

steward/monitors/runner.py

@@ -36,7 +36,8 @@ async def run_monitor(monitor: Monitor) -> dict:
         elif monitor.type == MonitorType.tcp.value:
             result.update(await tcp_check(monitor.target, int(cfg.get("port") or DEFAULT_TCP_PORT)))
         elif monitor.type == MonitorType.dns.value:
-            result.update(await dns_check(monitor.target, cfg.get("expected_ip") or None))
+            result.update(await dns_check(monitor.target, cfg.get("expected_ip") or None,
+                                         cfg.get("resolver") or None))
         elif monitor.type == MonitorType.http.value:
             result.update(await http_check(
                 url=monitor.target,