Introduce notifications app and integrate emails

Add a new notifications app (models, serializers, views, admin, tasks, consumers, routing, urls, tests) with Notification.notify for in-app websocket pushes and optional email delivery. Centralize email sending in notifications.tasks.send_email_with_context and re-export it from account.tasks for compatibility. Update account and commerce and advertisement tasks to use Notification.notify/_notify_order and the new email helper; adjust order/notification tasks to consolidate logic. Wire notifications into ASGI routing, settings and URL conf. Misc: handle OSError when importing weasyprint, add tmp/ to .gitignore, add local .claude PowerShell checks, add social.blog skeleton, and remove legacy ews-component test files.

backend/account/views.py

@@ -237,7 +237,9 @@ class UserView(viewsets.ModelViewSet):
 
     def get_serializer_class(self):
         user = getattr(self.request, 'user', None)
+
         is_admin = user and (getattr(user, 'role', None) == 'admin' or getattr(user, 'is_superuser', False))
+
         if self.action in ['retrieve', 'list'] and not is_admin:
             return PublicUserSerializer
         return CustomUserSerializer
@@ -277,11 +279,15 @@ class ChangePasswordView(APIView):
     def post(self, request):
         serializer = ChangePasswordSerializer(data=request.data)
         serializer.is_valid(raise_exception=True)
+
         user = request.user
+
         if not user.check_password(serializer.validated_data['current_password']):
             return Response({"current_password": "Nesprávné heslo."}, status=status.HTTP_400_BAD_REQUEST)
+        
         user.set_password(serializer.validated_data['new_password'])
         user.save()
+        
         return Response({"detail": "Heslo bylo úspěšně změněno."})