Add a qualified native macOS arm64 runtime and release

Problem

Stoat can compile selected host primitives on macOS, but it does not yet have a qualified native macOS runtime or release. Cross-compilation is insufficient evidence for VM lifecycle support.

Initial target

• Host: macOS arm64
• Accelerator: QEMU HVF
• Guest: Ubuntu arm64 first, then Debian arm64
• Distribution: signed and documented native release artifact

Acceptance criteria

• Define and enforce the supported macOS and QEMU version floor from current primary sources.
• Add native process lifecycle, identity checks, private file handling, Unix control endpoints, dependency discovery, and seed-generation behavior.
• Select the correct firmware and arm64 cloud-image artifacts without changing Linux/amd64 behavior.
• Qualify create, start, SSH, recipe application, copy, sharing, stop/restart, and cleanup on real macOS arm64 hardware.
• Add a hosted or self-hosted hardware gate that records the exact host, QEMU, guest image, and Stoat build identities.
• Produce a signed release artifact with installation, upgrade, rollback, and uninstall documentation.
• Keep unsupported macOS configurations fail-closed with actionable diagnostics.

Out of scope

• macOS guests
• Intel macOS support until suitable hardware is available
• Cross-architecture emulation as a supported performance profile

Start by locating the existing native host, QEMU, cloud-image, release, and hardware-gate entry points; the issue does not name specific files or tests. Define the macOS arm64 qualification matrix from the acceptance criteria, then verify the lifecycle flows and signed artifact on real hardware while recording the required host, QEMU, guest image, and build identities.