Function resolve 

pub fn resolve(config: &XdgDirConfig) -> Result<ResolvedXdgDirs>

Resolve XDG user directories from the host.

For each enabled dir, tries in order:

1. Parse ~/.config/user-dirs.dirs
2. Call xdg-user-dir <NAME>
3. Fall back to ~/DirName
4. If path doesn’t exist on disk: None