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/backup.rs

@@ -136,6 +136,7 @@ impl Collector for BackupCollector {
             name: "backup_overall_status".to_string(),
             value: MetricValue::String(match overall_status {
                 Status::Ok => "ok".to_string(),
+                Status::Inactive => "inactive".to_string(),
                 Status::Pending => "pending".to_string(),
                 Status::Warning => "warning".to_string(),
                 Status::Critical => "critical".to_string(),
@@ -199,6 +200,7 @@ impl Collector for BackupCollector {
                 name: format!("backup_service_{}_status", service_name),
                 value: MetricValue::String(match service_status {
                     Status::Ok => "ok".to_string(),
+                    Status::Inactive => "inactive".to_string(),
                     Status::Pending => "pending".to_string(),
                     Status::Warning => "warning".to_string(),
                     Status::Critical => "critical".to_string(),