pub fn config_dir() -> Result<PathBuf>
Where admin login keeps its state and --save writes token files. BUS_CONFIG_DIR, else $XDG_CONFIG_HOME/ai-crew-sync, else <home>/.config/ai-crew-sync (see home_dir).
admin login
--save
BUS_CONFIG_DIR
$XDG_CONFIG_HOME/ai-crew-sync
<home>/.config/ai-crew-sync
home_dir