fix(pos): исправить загрузку витринных комплектов

- Добавить display_name в CustomUser (name или email)
- Исправить get_showcase_kits_api: заменить username на display_name
- Использовать Case/When с output_field для выбора имени на уровне БД

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

myproject/pos/views.py

@@ -4,7 +4,7 @@ from django.contrib.auth.decorators import login_required
 from django.http import JsonResponse
 from django.views.decorators.http import require_http_methods
 from django.db import transaction
-from django.db.models import Prefetch, OuterRef, Subquery, DecimalField
+from django.db.models import Prefetch, OuterRef, Subquery, DecimalField, F, Case, When, CharField
 from django.db.models.functions import Coalesce
 from django.utils import timezone
 from django.core.exceptions import ValidationError
@@ -454,10 +454,18 @@ def get_showcase_kits_api(request):
         product_kit_id__in=kit_ids,
         cart_lock_expires_at__gt=timezone.now(),
         status='reserved'
-    ).select_related('locked_by_user').values(
+    ).select_related('locked_by_user').annotate(
+        # На уровне БД выбираем: если name есть - берем name, иначе email
+        locked_by_user_display=Case(
+            When(locked_by_user__name__isnull=False, then=F('locked_by_user__name')),
+            When(locked_by_user__name='', then=F('locked_by_user__email')),
+            default=F('locked_by_user__email'),
+            output_field=CharField()
+        )
+    ).values(
         'product_kit_id',
         'locked_by_user_id',
-        'locked_by_user__username',
+        'locked_by_user_display',
         'cart_lock_expires_at'
     )
 
@@ -476,7 +484,7 @@ def get_showcase_kits_api(request):
             is_locked_by_me = lock_info['locked_by_user_id'] == request.user.id
             kit['is_locked'] = True
             kit['locked_by_me'] = is_locked_by_me
-            kit['locked_by_user'] = lock_info['locked_by_user__username']
+            kit['locked_by_user'] = lock_info['locked_by_user_display']
             kit['lock_expires_at'] = lock_info['cart_lock_expires_at'].isoformat()
         else:
             kit['is_locked'] = False