feat: set skip_reason on nagios_runner when no commands configured

When NagiosRunnerPlugin has no commands configured, set skip_reason before
returning False from initialize(). This allows PluginLoader to log INFO
(not WARNING) when the plugin is skipped.

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

tests/test_nagios_runner.py

@@ -0,0 +1,22 @@
+import asyncio
+import logging
+import os
+import stat
+
+import pytest
+
+from hbd.client.plugins.nagios_runner import (
+    NagiosRunnerPlugin,
+    NAGIOS_OK,
+    NAGIOS_WARNING,
+    NAGIOS_CRITICAL,
+    NAGIOS_UNKNOWN,
+)
+
+
+def test_no_commands_sets_skip_reason():
+    plugin = NagiosRunnerPlugin(config={"commands": []})
+    result = asyncio.run(plugin.initialize())
+    assert result is False
+    assert plugin.skip_reason is not None
+    assert "nagios_runner.commands" in plugin.skip_reason