feat(runtime): ship precompiled macOS artifacts (#248)

* feat(runtime): ship precompiled macOS artifacts

- Add a versioned macOS arm64 runtime pack with deterministic feature selection and artifact verification.
- Link LLVM helper objects against release-built runtime and vendor inputs without compiling user-machine C.
- Wire package publishing, cache validation, documentation, and full-gate coverage for the new path.

* fix(runtime): harden precompiled artifact handling

* fix(runtime): make precompiled artifacts reproducible

* fix(runtime): reject opaque linkers from executable cache

* fix(runtime): normalize precompiled archive metadata

* fix(runtime): harden precompiled artifact caching

* fix(runtime): close executable cache link race

* fix(runtime): stage verified pack artifacts

* fix(runtime): bracket helper cache inputs

* fix(runtime): preserve executable link identity

* fix(runtime): trace selected linker dependencies