Implement Apple Container CLI runtime

[Richie Gomez (richiemsft)]

📖 Description

Implements PR 3 of the stacked Apple Container backend work. This adds bounded /usr/local/bin/container execution, explicit 0.8 policy validation, streaming stdio, timeout and kill handling, ownership-verified resource cleanup, kernel-lock-backed crash recovery, availability probing, and the qualified loopback-only guest-init image.

Seatbelt remains the default macOS process backend. Apple Container remains explicit and experimental, and unsupported policy fields fail closed. Samples, dedicated qualification CI, and final user documentation remain scoped to PRs 4 and 5.

🔗 References

Related PRs:

• Add Apple Container management layer #967
• Add Apple Container config surface #957

🔍 Validation

• Exact macOS arm64 release build and test package set
• macOS Clippy with warnings denied and Cargo formatting
• Apple Container unit tests and ignored real-runtime streaming integration test
• Allow, block, timeout, launch-failure, and SIGKILL recovery smoke coverage on Apple Container 1.2.2
• Windows x64 cross-target check and Clippy for affected crates
• Schema, generated SDK types, schema-version, and config validation gates
• Independent adversarial review and remediation pass

✅ Checklist

• Signed the Contributor License Agreement
• Linked to an issue
• Updated documentation (deferred to the dedicated stacked documentation PR)
• Updated Copilot instructions (final architecture documentation is deferred to the dedicated stacked documentation PR)
• If this PR changes Cargo.lock, the dependency-feed-check check passes (pending CI)

📋 Issue Type

• Bug fix
• Feature
• Task

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