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/entities/system/system.go

@@ -1,5 +1,7 @@
 package system
 
+// TODO: this is confusing, make common package with common/types common/helpers etc
+
 import (
 	"beszel/internal/entities/container"
 	"time"