fix(release): select host archive in release smoke

[JSONbored]

Summary

• install/use local cosign-compatible release smoke path by making the script select the host archive
• keep CI behavior on Linux while allowing macOS arm64 local release smoke to execute the matching release binary

What changed

• map uname OS/architecture to Nightward release asset names
• support tar.gz archives for Linux/macOS and zip archives for Windows shell environments
• add release-script fixture checks against hardcoded linux_amd64 smoke assets

Why

• local release verification should work without bypasses; after installing cosign, the previous script still downloaded a Linux amd64 binary that cannot execute on this macOS arm64 machine

Validation

• cosign version
• bash scripts/test-release-scripts.sh
• bash scripts/smoke-release-archive.sh v0.1.8
• trunk check --show-existing --fix --all
• trunk check --show-existing --all