chore(docker): native multi-arch app and indexer images

[gondoi]

Summary

• Migrate container builds to FuelLabs/github-actions/.github/workflows/docker-build-push.yml@master
• Native multi-arch: linux/amd64 + linux/arm64 (ubuntu-latest / ubuntu-24.04-arm)

Test plan

• CI passes on PR (amd64 + arm64 build jobs)
• Image manifest lists both architectures after merge

Part of DEVOPS-1249 / Move to graviton.

Depends on github-actions master with checkout/LFS inputs (DEVOPS-1248).

Made with Cursor

[cursor]

PR Summary

Medium Risk
Changes release and image-publish plumbing and depends on an external reusable workflow at @master; misconfiguration could break multi-arch pushes or skip indexer builds.

Overview
Removes the repo-local composite action .github/actions/docker-publish and replaces inline Docker build/push steps with the shared reusable workflow FuelLabs/github-actions/.github/workflows/docker-build-push.yml@master.

The workflow is split into separate jobs: check-docs and check-indexer (GHCR login + manifest check for the indexer image), then build-and-publish-app always runs the new pipeline for fuel-mcp-server, and build-and-publish-indexer runs only when docs changed or the indexer image is missing. Workflow-level permissions now include id-token: write for the new publish path.

Images are built with build-backend: native for linux/amd64 and linux/arm64 (amd64 on ubuntu-latest, arm64 on ubuntu-24.04-arm), with digest artifact keys app and indexer. Tagging behavior (branch, sha, semver) is preserved via the reusable workflow inputs.

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