feat: nagios operator for direct exit-code severity mapping

Add ComparisonOperator.NAGIOS ("nagios") that maps Nagios exit codes
directly to alert levels (0=OK 1=WARNING 2=CRITICAL 3=UNKNOWN) without
requiring numeric warning/critical thresholds. Hysteresis is bypassed for
discrete codes. Display template defaults to "{check_name}: {output}".
_format_display() handles None threshold_value gracefully.

Add nagios_runner.status_code as a built-in default threshold config so
nagios checks alert out of the box.

Also: fix alerts.html scrolling (override html,body), make hostname a link
to /plugins#<hostname>, remove overall_status/overall_status_code/plugin_count
from nagios_runner and hbc_mini, replace with computed worst-status in
plugins.html via nagiosWorstStatus() helper.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/hbc_mini.py

@@ -388,7 +388,6 @@ class NagiosRunnerPlugin(MonitorPlugin):
 
     async def _collect_metrics(self) -> Dict[str, Any]:
         results: Dict[str, Any] = {}
-        worst = 0
         for cmd_cfg in self.commands:
             name = cmd_cfg.get("name")
             command = cmd_cfg.get("command")
@@ -399,10 +398,6 @@ class NagiosRunnerPlugin(MonitorPlugin):
             results[f"{name}_status_code"] = rc
             results[f"{name}_output"] = msg
             results.update({f"{name}_{k}": v for k, v in perf.items()})
-            worst = max(worst, rc)
-        results["overall_status"] = _NAGIOS_STATUS.get(worst, "UNKNOWN")
-        results["overall_status_code"] = worst
-        results["plugin_count"] = len(self.commands)
         return results