ci: publish multi-arch container images

[IgnazioDS]

Summary

• set up QEMU in the image publish workflow
• set up Docker Buildx before image builds
• publish app-server, frontend, and query-engine images as linux/amd64,linux/arm64 multi-arch manifests

Fixes #139.

Why

The self-hosting compose files pull ghcr.io/lmnr-ai/* images without pinning a platform, but the current publish workflow builds only the default single-arch image variant. That leaves ARM hosts pulling amd64-only images and failing at runtime with exec format error, which matches the failure reports in #139.

This patch keeps the runtime and compose files unchanged and fixes the problem where it actually originates: the image publish pipeline.

Validation

• reviewed docker-compose.yml / docker-compose-full.yml to confirm the failing services pull ghcr.io/lmnr-ai/app-server and ghcr.io/lmnr-ai/frontend
• reviewed .github/workflows/build-push.yml to confirm the workflow currently omits Buildx/QEMU and does not set platforms
• docs/config only unaffected; this is a release-pipeline change

Note

After merge, maintainers will need a new release publish to republish the GHCR tags as multi-arch manifests.

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Note

Low Risk
Low risk: workflow-only changes to the release publish pipeline; main risk is longer builds or unexpected Buildx/QEMU issues affecting image publishing.

Overview
Updates the release build-push GitHub Actions workflow to publish multi-architecture Docker images.

The pipeline now sets up QEMU and Docker Buildx and builds/pushes images for linux/amd64 and linux/arm64 via docker/build-push-action, producing multi-arch manifests for the existing GHCR images.

^{Written by Cursor Bugbot for commit 7e5479b. This will update automatically on new commits. Configure here.}

[CLAassistant]

All committers have signed the CLA.

[dinmukhamedm]

@IgnazioDS can you please set the version to the latest v4 (uses later node)?

Also, please start the PR from the dev branch and target the dev branch.