feat(release): establish Go delivery MVP

[jmgilman]

Summary

• establish the shared Go release contract and reusable GitHub Release workflows
• add signed, attested multi-architecture OCI image production and GHCR publication
• provide a copyable consumer example plus adoption, rehearsal, recovery, upgrade, and reference documentation

Verification

• cross-repository GitHub Release and GHCR rehearsals completed successfully
• exact-identity Cosign, GitHub provenance, and registry-backed SPDX verification passed
• actionlint, GoReleaser validation, documentation link checks, git diff --check, and all Moon tasks passed

Scope

This intentionally lands the current MVP. Homebrew, MacPorts, Nix, Scoop, generalized installer, and mise distribution remain future delivery-channel work.