fix: align UserGroup ReBAC syncing with Tenant namespace design

backend/internal/service/org_chart_service.go

@@ -130,9 +130,9 @@ func (s *orgChartService) ImportCSV(ctx context.Context, tenantID string, r io.R
 
 		// 3. Sync Membership to Keto via Outbox
 		if s.ketoOutboxRepo != nil {
-			// Add as member of UserGroup
+			// Add as member of UserGroup (which is a Tenant namespace object)
 			_ = s.ketoOutboxRepo.Create(ctx, &domain.KetoOutbox{
-				Namespace: "UserGroup",
+				Namespace: "Tenant",
 				Object:    leafID,
 				Relation:  "members",
 				Subject:   "User:" + kratosID,
@@ -142,7 +142,7 @@ func (s *orgChartService) ImportCSV(ctx context.Context, tenantID string, r io.R
 			// Add as owner if applicable
 			if isOwner {
 				_ = s.ketoOutboxRepo.Create(ctx, &domain.KetoOutbox{
-					Namespace: "UserGroup",
+					Namespace: "Tenant",
 					Object:    leafID,
 					Relation:  "owners",
 					Subject:   "User:" + kratosID,