Arm64 Support for SF Releases (binary and images)

[excalq]

Summary

Add multi-arch image publishing support for Nitro, with native linux/amd64 and linux/arm64 builds and a manifest that publishes a single tag for both architectures. This is primarily to support running the service on AWS Graviton instances.

Why

• We want to run this service on AWS Graviton (linux/arm64).
• The existing release path assumed only one architecture in a few places and used hardcoded amd64 asset naming.
• Building arm64 via emulation is too slow/unreliable for this repo, so we use native runners and merge the results into a multi-arch manifest.

What changed

• Makefile
  • docker now passes --platform $(ARCH) to docker build
  • default ARCH is linux/amd64
• .github/workflows/sf_release.yml
  • builds on ubuntu-24.04 and ubuntu-24.04-arm
  • builds per-arch images for linux/amd64 and linux/arm64
  • publishes a multi-arch manifest tag
  • extracts release binaries for both architectures
  • lowercases the image name before tagging to avoid GHCR invalid-tag failures when the org name contains uppercase characters

Notes

• This keeps the release flow compatible with GHCR.
• The multi-arch manifest is created from native per-arch images rather than QEMU-emulated builds.
• The release artifacts now include both nitro_linux_amd64 and nitro_linux_arm64.
  Testing
• Workflow was updated and pushed on a dedicated branch.
• Tested on the fork's GitHub-hosted action runners. Result packages

[maoueh]

Merged via #26, thanks!