Generalize the base image from audit mode, with hibernation off

The answer file now boots into audit mode after Setup instead of logging on
as the built-in Administrator with a password: no account or credentials in
the answer file, and no copy of one left in C:\Windows\Panther. The auditUser
commands disable the built-in Administrator, turn hibernation off (no
hiberfil.sys in the image), remove cached answer files and setup logs, and run
sysprep /generalize.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -117,9 +117,9 @@ does not run Windows Setup again. `build-windows-base.sh` makes that base image
 (by default at the path `./download-images.sh --print-path windows11` prints): it
 installs Windows unattended from the ISO in `install-iso/` (it does everything
 itself: answer file in `windows11/seed/`, QEMU hardware in `windows11/qemu/`; this
-directory has no dependency on any other repository). The answer file logs on once
-with the built-in Administrator, which it disables again, and runs
-`sysprep /generalize` as its last step; the script waits for the guest to power
+directory has no dependency on any other repository). The answer file boots
+into audit mode (no account and no credentials are needed) and runs
+`sysprep /generalize` there as its last step; the script waits for the guest to power
 off and stores the disk read-only. The image is clean and generic, like a cloud
 image: nothing but Windows, with no account, no SSH, no settings, no VirtIO or
 other hardware-specific drivers and no machine identity. Each VM is configured