refactor: optimize system updates and create systems package

- Created SystemManager to handle system lifecycle and events
- Created tests for system management operations
- Added test helpers for creating and managing test systems
- Introduced optional port configuration in system config

beszel/internal/hub/config.go

@@ -22,7 +22,7 @@ type Config struct {
 type SystemConfig struct {
 	Name  string   `yaml:"name"`
 	Host  string   `yaml:"host"`
-	Port  uint16   `yaml:"port"`
+	Port  uint16   `yaml:"port,omitempty"`
 	Users []string `yaml:"users"`
 }