Attach universal macOS binary to GitHub releases

[schneiderandre]

Summary

• Adds a build job to the release workflow that compiles a universal macOS binary (arm64 + x86_64) and uploads it as a release asset (pfw-macos-universal.tar.gz).
• Slack notification jobs now depend on the build job via needs: build.
• Enables installing pfw directly from a GitHub release via tools like mise (GitHub backend), without needing Homebrew or building from source.

Considerations

• Universal binary: Builds for both arm64 and x86_64 in a single binary. I assume you still want to support Intel Macs.
• Build job: Only runs on release events. Uses gh release upload to attach the tarball directly to the triggering release.
• needs: build: The Slack notification jobs depend on the build job. Notifications are only sent after the binary has been successfully built and uploaded.

Verification

A test release (0.0.7) was created to verify the workflow. The binary was successfully built, uploaded, and installed via mise:

mise use -g github:schneiderandre/pfw@0.0.7

[stephencelis]

Thanks!