fix(packages): enforce Intel macOS retirement

[dongkeren]

Summary

Close the libnode side of the product-wide Intel macOS retirement by making the supported package matrix explicit and fail-closed.

Related delivery

• Kungfu ADR: fix(platform): retire Intel macOS product surfaces kungfu#2105
• Assignment: 019fbbc3-f2e0-7080-b821-2989eb71e0f4

Changes

• verify exactly four supported package identities: Darwin ARM64, Linux ARM64, Linux x64, and Windows x64
• keep Darwin x64 explicitly unsupported at the package entrypoint
• scan every active build, release, package, and KFD surface for retired Intel macOS identities
• run the platform-retirement policy in the required Buildchain verify lifecycle

The latest protected base already withdrew the Darwin x64 build and publication rows. This PR adds the product-owned regression boundary that prevents those surfaces from returning.

Verification

• GITHUB_ACTIONS=true corepack pnpm verify-kfd-witnesses
• corepack pnpm verify-platform-policy
• buildchain lifecycle run verify --required
• moving-base replay plus git range-diff

Checklist

• Commits are signed off (DCO)
• Public documentation preserves the unsupported-platform contract
• KFD witnesses are current

[kungfu-origin]

Reviewed the current protected-base diff: it adds an exact four-platform package policy, explicit Darwin x64 rejection, active-surface regression scanning, and required Buildchain verification without widening release claims.