Retire s6 and complete the distro transition to dinit #633

Mere Linux will use dinit as its init and service manager and retire s6 support. The distro owns this decision; the mere package manager implements its required behavior. Keep utmps and skalibs where independently required.

Work:

• QEMU guest test harness and Mere shell/build execution: Add a reproducible QEMU guest test harness #635 (through Exercise Mere shell and offline builds in the QEMU guest #639).
• Bootable Mere/dinit test system, boot services, and recipe changes: Establish and validate a dinit-based Mere test system #634.
• Package-manager integration, s6 removal, and package-manager documentation: Complete package-manager integration for the dinit-only distro mere#63.
• Finish distro recipe/documentation cleanup and review end-user image-tool needs after replacement behavior is validated.

Each linked issue owns its acceptance criteria. Merge status alone is not runtime evidence. Validation covers lifecycle, boot intent separately from live state, status/logs, package install/upgrade/removal, generation activation/rollback, and shutdown/reboot.

Constraints:

• The harness is developer test tooling, separate from end-user installation/image tools. Use POSIX shell where practical.
• Mere boot does not use an initramfs; do not add one without a concrete requirement. A test-only initramfs is acceptable. Direct QEMU kernel loading does not validate a bootloader.
• The legacy disk_image and mkinitramfs scripts use pacman, host loop devices/mounts and extlinux. They are historical references only.
• Discuss remaining boot-policy and migration decisions with the maintainer before implementation.

Status: boot, recovery and stopped-service lifecycle have local guest evidence in #634. The essential-service and running-service behavior in jhuntwork/mere#76 has no guest validation yet. Outstanding: that validation, broader failure coverage, and s6 removal.