Drop the manual make -C opcodes i386-gen call from pass1.sh and rely on default_src_compile instead.
This avoids failures when opcodes/ is not yet available in the current build context (make: *** opcodes: No such file or directory) and matches the stable top-level recursive build flow used elsewhere in the project.
- add --stage0-image in rootfs.py for qemu to boot an existing kernel-bootstrap image
- when --stage0-image is combined with --build-guix-also, update BUILD_GUIX_ALSO in image config and sync /steps-guix into the image
- require stage0 /init to contain guix handoff marker instead of patching /init implicitly
- add run_steps_guix_if_requested() to make_bootable-generated /init so rebooted stage0 images can enter steps-guix directly
- run /steps-guix/0.sh with bash in after.sh
- make script-generator start mode convention-based: /steps stays kaem-first, alternate roots (e.g. /steps-guix) start in bash
- remove redundant explicit /steps config-root argument from seed/preseeded/reconfigure script-generator calls
