feat: nagios_runner improvements and alerts page fixes

- nagios_runner: remove overall_status/overall_status_code/plugin_count fields;
  each command still reports its own <name>_status and <name>_status_code
- threshold: expose {output} and {status} aliases in display templates for
  nagios_runner generic matches (mapped from <check_name>_output/status)
- alerts.html: fix scrolling by overriding html,body height/overflow (style.css
  sets both); make hostname a link to /plugins/<hostname>

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

hbd/server/threshold.py

@@ -1152,6 +1152,19 @@ class ThresholdChecker:
         # Add all plugin data fields if available
         if plugin_data:
             format_context.update(plugin_data)
+
+        # For nagios_runner generic matches, expose the matched check's output
+        # and status as short aliases {output} and {status} so display templates
+        # don't need to use the full {check_disk_root_output} form.
+        if check_name and plugin_data:
+            if 'output' not in format_context:
+                output = plugin_data.get(f"{check_name}_output")
+                if output is not None:
+                    format_context['output'] = output
+            if 'status' not in format_context:
+                status = plugin_data.get(f"{check_name}_status")
+                if status is not None:
+                    format_context['status'] = status
         
         try:
             # Format the display string