Switch to SysVinit init system

- Changed init system from systemd to sysvinit as requested
- Updated package list: live-config-sysvinit, sysvinit
- Kept debian-keyring and debian-archive-keyring for proper verification
- Removed problematic devuan-keyring hook to avoid bootstrap conflicts
- Updated README to reflect sysvinit usage
- Maintained all other functionality (SSH, OpenVPN, auto-start, etc.)