add a mini editor

There's cases where I'd want to just quickly edit a file in conflicto instead of opening a full fledged editor, a simple syntax highlight is enough, don't need auto complete or AI support here, just a very simple editor that can edit some files.

The issue does not name files or tests. Start by locating the existing diff-viewer and file-opening entry points in the JavaScript/Preact/Wails app, then determine how edited files are saved. Done means supported files can be edited in a simple syntax-highlighted editor without autocomplete or AI features.

Written by the indexing model from the issue text.