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/common_test.go

@@ -7,6 +7,7 @@ import (
 	"encoding/json"
 	"io"
 	"net/http"
+	"slices"
 	"time"
 )
 
@@ -94,11 +95,8 @@ func (m *mockAuditRepo) FindByUserAndEvents(ctx context.Context, userID string,
 	var results []domain.AuditLog
 	for _, log := range m.logs {
 		if log.UserID == userID {
-			for _, et := range eventTypes {
-				if log.EventType == et {
-					results = append(results, log)
-					break
-				}
+			if slices.Contains(eventTypes, log.EventType) {
+				results = append(results, log)
 			}
 		}
 	}