Homebrew formula

[johnnyhuy]

Summary

• Publish Homebrew formula for macOS installs.

Context

• Homebrew is the primary macOS distribution channel.

Scope

• Create formula pointing to GitHub release assets.
• Use SHA256 checksums for validation.
• Support arm64 and x64 variants.
• Document brew tap and install instructions.

Out of scope

• Brew cask and GUI bundles.

Acceptance criteria

• brew install skillet works on both macOS arch variants.