Fix cross-target release package coverage

[chubes4]

Summary

• separate cross-target package structure validation from target-native process execution
• keep packaged CLI execution mandatory when the release target matches the host
• centralize and test Node-to-release platform normalization
• include the focused compatibility test in Homeboy release gates

Fixes #2250.

Verification

• npm run test:release-target
• npm run test:sharp-release-runtime
• npm run build
• npm run smoke -- --group package (Docker-backed mysqli E2E skipped because Docker is unavailable)
• npm run test:release-package-coverage
• npm run release:package
• git diff --check

On macOS ARM64, release package coverage now validates the Linux x64 package and reports:

Skipping packaged CLI execution because release target linux-x64 does not match host darwin-arm64.
release package coverage passed

Linux x64 remains responsible for the packaged --version, commands, and wrapper execution assertions because its host and target match.

AI assistance

OpenAI GPT-5.6 Sol via OpenCode was used to reproduce and diagnose the release-gate failure, implement the compatibility boundary and tests, and run verification. Chris Huber reviewed and remains responsible for every line.