Add GoReleaser release pipeline

Introduces a GoReleaser Pro v2 config plus a GitHub Actions workflow that publishes signed, notarized darwin/linux binaries on tag push (or manual dispatch). Releases also publish a Homebrew cask via the entireio/homebrew-tap repository.

Version, commit, and build date are injected at link time into the versioninfo package added in the previous commit, so git-sync version reports the real release identity. The workflow notifies Slack on failure and ignores the dist/ build output.