## Description The `docker_build` job does not specify a `--platform` flag, meaning the image architecture silently depends on whichever runner picks up the job. On an ARM runner this produces an ARM image tagged and published as the release image, breaking amd64 users pulling `latest`. Building an explicit multi-arch manifest ensures the image runs correctly on both amd64 and arm64 hosts. ## Acceptance Criteria - `docker_build` uses Docker Buildx to produce a multi-arch manifest covering `linux/amd64` and `linux/arm64`. - The published image runs correctly on both amd64 and arm64 hosts. - The `--platform` flag (or equivalent buildx setup) is explicit so the build is never silently architecture-dependent. ## Additional information The missing `--platform` flag is also a correctness issue in the current pipeline when community ARM runners are enabled — not just a missing feature. Fixing this is a prerequisite for safely allowing `docker_build` to run on ARM runners.