Add cross-platform release assets

[itamaker]

Summary

• publish Linux and Windows CLI archives alongside the existing macOS release assets
• keep the artifact naming, checksums, and archive contents aligned with the other managed Go repos
• refresh the README preview artwork and document that GUI release binaries remain macOS-focused

Verification

• go test ./...
• go build ./cmd/go-chrome-ai
• GOOS=linux/windows cross-builds for ./cmd/cli
• goreleaser check
• goreleaser release --snapshot --clean --skip=publish