* Add Pacman settings submenu with Color and ParallelDownloads
Replace the standalone Parallel Downloads menu item with a Pacman
submenu containing ParallelDownloads (default 5) and Color (default on).
Settings are applied to both live and target system pacman.conf.
Hidden behind --advanced flag.
Backward compatible with old configs using "parallel_downloads" key.
* Skip _apply_to_live when user exits Pacman menu without changes
* Use TypedDict for PacmanConfiguration serialization
* Show Pacman menu by default, keep ParallelDownloads behind --advanced