Add macOS Apple Silicon (.pkg) Support

[AlexGRDev]

This Pull Request introduces packaging support for a native macOS Apple Silicon installer (.pkg) for Zeronsd.

It enables easier installation for users running:

• Apple Silicon (M1 / M2 / M3 / M4 / M5)
• macOS Ventura / Sonoma / Sequoia or newer
• Architecture: aarch64-apple-darwin

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Installer for maintainers to test

Download the PKG installer here:

https://github.com/AlexGRDev/zeronsd/releases/download/v1.3.0-macos-arm64/zeronsd-macos-arm64-1.3.0.pkg

This installer places the zeronsd binary in:
/opt/homebrew/bin/zeronsd

---

Installation Test Instructions

To install on macOS:

sudo installer -pkg zeronsd-macos-arm64-1.3.0.pkg -target /
zeronsd --version

Included in this PR

•	Added docs/BUILD_MACOS.md with build and packaging instructions
•	No modifications to Zeronsd core logic
•	This PR only adds documentation and external binary packaging for macOS Apple Silicon

Possible future improvements

If maintainers are interested, I can also contribute:
• GitHub Actions automation to build and publish .pkg on each release
• Linux ARM64 .deb installer (Raspberry Pi, Debian, Ubuntu)
• Optional .dmg auto-install variant
• Universal macOS package (Intel + ARM)

Thanks for reviewing!

[CLAassistant]

All committers have signed the CLA.