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/logger/client_log_policy.go

@@ -104,11 +104,11 @@ func SanitizeClientLogMessage(message string) string {
 	return sanitized
 }
 
-func SanitizeClientLogData(data map[string]interface{}) map[string]interface{} {
+func SanitizeClientLogData(data map[string]any) map[string]any {
 	if len(data) == 0 {
 		return data
 	}
-	out := make(map[string]interface{}, len(data))
+	out := make(map[string]any, len(data))
 	for k, v := range data {
 		if isSensitiveClientLogKey(k) {
 			out[k] = "*****"
@@ -119,12 +119,12 @@ func SanitizeClientLogData(data map[string]interface{}) map[string]interface{} {
 	return out
 }
 
-func sanitizeClientLogValue(v interface{}) interface{} {
+func sanitizeClientLogValue(v any) any {
 	switch val := v.(type) {
-	case map[string]interface{}:
+	case map[string]any:
 		return SanitizeClientLogData(val)
-	case []interface{}:
-		next := make([]interface{}, len(val))
+	case []any:
+		next := make([]any, len(val))
 		for i := range val {
 			next[i] = sanitizeClientLogValue(val[i])
 		}