Wire three Command menu items that open TLC's config files in
the built-in editor: extensions, user menu, and file highlighting
rules. Files are created empty if they don't exist.
Cmd::EditExtensionFile → ~/.config/tlc/extensions
Cmd::EditMenuFile → ~/.config/tlc/menu
Cmd::EditHighlightFile → ~/.config/tlc/filehighlight.ini
Added open_config_file() helper in dialog_ops.rs that resolves
the config dir via ProjectDirs, creates parent + empty file if
missing, then opens the editor.
Command menu now has all 20 items (was 17/20).
vasilito
eb8686f4c3