Add Status::Inactive for inactive services with empty circle display

- Add new Status::Inactive variant to enum for better service state representation
- Agent now assigns Status::Inactive instead of Status::Warning for inactive services
- Dashboard displays inactive services with empty circle (○) icon in gray color
- User-stopped services still show as Status::Ok with green filled circle
- Inactive services treated as OK for host status aggregation
- Improves visual clarity between active (●), inactive (○), and warning (◐) states

agent/src/collectors/systemd.rs

@@ -372,7 +372,8 @@ impl SystemdCollector {
                     debug!("Service '{}' is inactive but marked as user-stopped - treating as OK", service_name);
                     Status::Ok
                 } else {
-                    Status::Warning
+                    debug!("Service '{}' is inactive - treating as Inactive status", service_name);
+                    Status::Inactive
                 }
             },
             "failed" | "error" => Status::Critical,