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/user_projection_sync_service.go

@@ -110,7 +110,7 @@ func MapKratosIdentityToLocalUser(identity KratosIdentity) domain.User {
 	return user
 }
 
-func kratosProjectionTraitString(traits map[string]interface{}, key string) string {
+func kratosProjectionTraitString(traits map[string]any, key string) string {
 	if traits == nil {
 		return ""
 	}
@@ -124,14 +124,14 @@ func kratosProjectionTraitString(traits map[string]interface{}, key string) stri
 	return fmt.Sprint(value)
 }
 
-func kratosProjectionTraitStringArray(traits map[string]interface{}, key string) []string {
+func kratosProjectionTraitStringArray(traits map[string]any, key string) []string {
 	if traits == nil {
 		return nil
 	}
 	switch value := traits[key].(type) {
 	case []string:
 		return value
-	case []interface{}:
+	case []any:
 		items := make([]string, 0, len(value))
 		for _, item := range value {
 			if str, ok := item.(string); ok && strings.TrimSpace(str) != "" {