fix(user-management): pagination, duplicate profile creation, type fixes

backend/auth_app/serializers.py

@@ -88,7 +88,8 @@ class UserCreateSerializer(serializers.ModelSerializer):
     def create(self, validated_data):
         role = validated_data.pop('role', 'trainer')
         user = User.objects.create_user(**validated_data)
-        UserProfile.objects.create(user=user, role=role)
+        user.profile.role = role
+        user.profile.save(update_fields=['role'])
         return user