Hidden items

Currently, all items have the same definition. They are also used as variables. If we ever decide to show players the items they carry, we only want to display "actual" items and hide the pure variables.

Start by locating the item definition and the code that uses items as variables. Clarify how an “actual” item should be distinguished from a pure variable and where carried items would be displayed. Done means the model and display behavior consistently exclude pure variables, but this issue names no files or tests.

Written by the indexing model from the issue text.