When dismounting via CLI (/d /q /s), SHChangeNotify is called without
SHCNF_FLUSH flag, making it asynchronous. The process exits before
Explorer processes the notification, leaving a phantom drive letter
visible in Explorer as an inaccessible Local Disk until reboot.
Add SHCNF_FLUSH in Silent (CLI) mode to force synchronous shell
notification processing in both single-volume (UnmountVolumeBase)
and dismount-all (DismountAll) code paths. The flush is only added
in CLI mode to avoid adding latency to interactive GUI operations.
Co-authored-by: Contributor <contributor@example.com>
