ci: publish multi-arch Docker images for amd64 + arm64

[goldytech]

Summary

This PR enables official multi-arch image publishing so OpenWA tags can be pulled natively on both x64 and ARM64 hosts.

Closes #164

Changes

• Add platforms: linux/amd64,linux/arm64 to Docker build/push in CI workflow
• Add platforms: linux/amd64,linux/arm64 to Docker build/push in release workflow
• Document supported image architectures in README
• Align DevOps guide CI snippet with the workflow changes

Why

ARM64 environments (Apple Silicon and ARM VPS) need official multi-arch manifests for seamless image pulls using the same tag.

Scope

This change only updates image build/publish configuration and related documentation; no runtime behavior changes.

Validation

• Workflow syntax updated in existing docker/build-push-action steps only
• No changes to application code paths

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds explicit multi-architecture (amd64 + arm64) Docker image builds/publishing and documents the supported GHCR platforms.

Changes:

• Configure Docker build/push steps to publish multi-arch manifests (linux/amd64, linux/arm64) in CI and release workflows.
• Update infrastructure docs and README to reflect the official multi-arch GHCR images.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
docs/10-devops-infrastructure.md	Documents multi-arch build configuration in the infrastructure guide.
README.md	States the supported multi-arch platforms for GHCR images.
.github/workflows/release.yml	Publishes multi-arch images on release.
.github/workflows/ci.yml	Publishes multi-arch images during CI.

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[goldytech]

Addressed review feedback in commit 0efae98:\n\n- Added docker/setup-qemu-action@v3 before Buildx in CI and release Docker jobs for reliable ARM64 builds on GitHub runners.\n- Centralized platform configuration using workflow env DOCKER_PLATFORMS=linux/amd64,linux/arm64 and referenced it in build-push steps.\n\nBoth review threads are now resolved.