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/handler/client_tenant_access.go

@@ -17,9 +17,9 @@ const (
 	clientAllowedTenantsKey         = "allowed_tenants"
 )
 
-func normalizeClientTenantAccessMetadata(metadata map[string]interface{}) (map[string]interface{}, error) {
+func normalizeClientTenantAccessMetadata(metadata map[string]any) (map[string]any, error) {
 	if metadata == nil {
-		metadata = map[string]interface{}{}
+		metadata = map[string]any{}
 	}
 
 	restricted := readMetadataBoolValue(metadata, clientTenantAccessRestrictedKey)
@@ -49,7 +49,7 @@ func normalizeClientTenantAccessMetadata(metadata map[string]interface{}) (map[s
 	return metadata, nil
 }
 
-func clientTenantAccessRestricted(metadata map[string]interface{}) bool {
+func clientTenantAccessRestricted(metadata map[string]any) bool {
 	if metadata == nil {
 		return false
 	}
@@ -59,7 +59,7 @@ func clientTenantAccessRestricted(metadata map[string]interface{}) bool {
 	return len(normalizeMetadataStringSlice(metadata[clientAllowedTenantsKey])) > 0
 }
 
-func clientAllowedTenants(metadata map[string]interface{}) []string {
+func clientAllowedTenants(metadata map[string]any) []string {
 	if metadata == nil {
 		return nil
 	}