refactor: remove Health Monitor plugin - heartbeat built into core (#115)

The health monitor/Grafana heartbeat is mandatory infrastructure that
must always be active. The core system plugin (plg_system_mokowaas)
already has handleGrafanaProvisioning() and sendHeartbeat(), making
the separate monitor plugin redundant.

- Removed plg_system_mokowaas_monitor from package manifest
- Removed from script.php enable/protect lists
- Removed from cascade enable/disable logic
- Removed from dashboard plugin metadata
- Excluded from dashboard plugin discovery query
- Disabled on dev server (can be uninstalled manually)

Health monitoring is now entirely handled by the core plugin which
is protected and cannot be disabled.

Authored-by: Moko Consulting
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/script.php

@@ -41,7 +41,6 @@ class Pkg_MokowaasInstallerScript
 		$this->enablePlugin('system', 'mokowaas_firewall');
 		$this->enablePlugin('system', 'mokowaas_tenant');
 		$this->enablePlugin('system', 'mokowaas_devtools');
-		$this->enablePlugin('system', 'mokowaas_monitor');
 		$this->enablePlugin('webservices', 'mokowaas');
 		$this->enablePlugin('task', 'mokowaasdemo');
 		$this->enablePlugin('task', 'mokowaassync');
@@ -211,7 +210,6 @@ class Pkg_MokowaasInstallerScript
 				$db->quote('mokowaas_firewall'),
 				$db->quote('mokowaas_tenant'),
 				$db->quote('mokowaas_devtools'),
-				$db->quote('mokowaas_monitor'),
 				$db->quote('com_mokowaas'),
 				$db->quote('mod_mokowaas_cpanel'),
 				$db->quote('mokowaasdemo'),