supermachine-kernel-x86-64 0.7.68

Pre-built x86_64 Linux microVM kernel (minimal config), busybox, and in-VM agent for supermachine's KVM backend, bundled as xz-compressed payloads inside the crate (no network at build time). Resolved automatically per target by the `supermachine-kernel` facade; pin in lockstep with `supermachine`.