feat: add role field to user serializer for menu control

- Endpoint /me/ now returns 'role': 'administrator' or 'role': 'user'
- Uses Django's is_staff to determine administrator role

tienda_ilusion/users/serializers.py

@@ -3,6 +3,11 @@ from rest_framework import serializers
 
 
 class UserSerializer(serializers.ModelSerializer):
+    role = serializers.SerializerMethodField()
+
     class Meta:
         model = User
-        fields = ('id', 'username', 'email', 'first_name', 'last_name')
+        fields = ('id', 'username', 'email', 'first_name', 'last_name', 'role')
+
+    def get_role(self, obj):
+        return 'administrator' if obj.is_staff else 'user'