feat(user): support fixed UUID registration and enhance bulk import results

- Added support for fixed UUIDs during bulk registration (Search-first + ExternalID mapping)
- Implemented idempotency and visibility restoration for soft-deleted users
- Enhanced bulk upload UI to show 'New/Updated/Unchanged' status and modified fields
- Added logic to reclaim identifiers (login_id) from colliding records
- Added frontend E2E and backend unit tests for UUID integrity and conflict handling
- Fixed i18n, formatting, and mock tests to satisfy code-check
- Applied 'go fix' for 'omitzero' tags and general Go standards

backend/internal/service/keto_service.go

@@ -110,7 +110,7 @@ func (s *ketoService) CheckPermission(ctx context.Context, subject, namespace, o
 	maxRetries := 5
 	backoff := 200 * time.Millisecond
 
-	for i := 0; i < maxRetries; i++ {
+	for i := range maxRetries {
 		req, _ := http.NewRequestWithContext(ctx, "GET", u.String(), nil)
 		resp, err := s.client.Do(req)
 		if err == nil {
@@ -143,7 +143,7 @@ func (s *ketoService) CheckPermission(ctx context.Context, subject, namespace, o
 
 func (s *ketoService) CreateRelation(ctx context.Context, namespace, object, relation, subject string) error {
 	u := fmt.Sprintf("%s/admin/relation-tuples", s.writeURL)
-	payload := map[string]interface{}{
+	payload := map[string]any{
 		"namespace":  namespace,
 		"object":     object,
 		"relation":   relation,
@@ -156,7 +156,7 @@ func (s *ketoService) CreateRelation(ctx context.Context, namespace, object, rel
 	maxRetries := 5
 	backoff := 200 * time.Millisecond
 
-	for i := 0; i < maxRetries; i++ {
+	for i := range maxRetries {
 		req, _ := http.NewRequestWithContext(ctx, "PUT", u, bytes.NewReader(body))
 		req.Header.Set("Content-Type", "application/json")
 
@@ -197,7 +197,7 @@ func (s *ketoService) DeleteRelation(ctx context.Context, namespace, object, rel
 	maxRetries := 5
 	backoff := 200 * time.Millisecond
 
-	for i := 0; i < maxRetries; i++ {
+	for i := range maxRetries {
 		req, _ := http.NewRequestWithContext(ctx, "DELETE", u.String(), nil)
 		resp, err := s.client.Do(req)
 		if err == nil {