Ignore data files for gitignore.user

When creating gitignore.user, I forgot to pay attention to the individual module gitignore files... which means we are not ignoring data files. That's bad. We want to ignore those, but we probably don't want to ignore everything in the data folders and all the same things that we ignore in the main repository.

Start by comparing gitignore.user with the individual module gitignore files and the main repository rules. Identify the data-file patterns that should be added without ignoring every file in data folders or duplicating all main-repository exclusions. Done means the intended data files are ignored while unrelated data-folder contents remain available.

Written by the indexing model from the issue text.