### **Summary** Extend the GitLab CI pipeline to build **`linux/arm64` (AArch64)** variants of the base container alongside existing `linux/amd64` builds, enabling compatibility with Apple Silicon, Nvidia Grace, and Arm Neoverse V2 environments. ### **Details** * The current pipeline only runs on amd64 GitLab runners and produces x86_64 images. * Add a parallel CI job capable of building the same Dockerfile for `linux/arm64` using either: * A native **Arm runner** (preferred), or * **QEMU + Docker Buildx** emulation on the existing amd64 runner. * Push the resulting image as: ``` codecr.jlab.org/scicomp/software/jlab-container-docs/jlab-base:<tag>-arm64 ``` * Update the manifest-merge job to produce a multi-architecture index manifest referencing both amd64 and arm64 images. * Verify successful creation of the manifest list using `skopeo inspect`. ### **Acceptance Criteria** * CI successfully produces two image variants: `linux/amd64` and `linux/arm64`. * A combined manifest list (`index digest`) exists for the final tag. * Pulling the image on either x86_64 or Arm hosts retrieves the correct architecture automatically. * Pipeline documentation updated to note Arm build requirements for Mac users and QEMU setup.