Add Apple Silicon (darwin/arm64) release binaries

[denniswebb]

Problem

The release workflow (release.yml) only builds binaries for 386 and amd64 architectures. Apple Silicon Macs (M1/M2/M3/M4) use arm64, so there is no native binary for them. Users on Apple Silicon must run the amd64 binary through Rosetta 2.

The Docker job already builds linux/arm64, but the Go binary matrix and Homebrew formula do not include darwin/arm64.

Current matrix

OS	Arch
linux	386, amd64
windows	386, amd64
darwin	amd64

Proposed changes

1. Add arm64 to the goarch matrix and exclude arm64 for windows (and optionally linux/386 if desired)
2. Update the Homebrew formula to support both darwin-amd64 and darwin-arm64 (requires a multi-arch Homebrew tap or on_arm/on_intel blocks)
3. Optionally add linux/arm64 binaries as well

Impact

Apple Silicon has been the default Mac architecture since late 2020. Native binaries avoid Rosetta overhead and are expected by most macOS users today.