ci: publish host-specific arm64e stage1 assets

[cypherair]

Summary

• publish separate aarch64 and x86_64 host stage1 toolchains for the stable196 arm64e prerelease
• keep the extracted stage1-arm64e-patch layout while renaming release assets to rust-stage1-for-arm64e-.*
• assert the actual rustc host triple at runtime instead of trusting runner labels blindly

Validation

• ruby YAML parse for .github/workflows/arm64e-stage1-prerelease.yml
• git diff --check
• dry-run workflow_dispatch with create_release=false pending