feat(infra): Publish Docker images on release

[andrey-fomin]

Provide an official Docker Hub distribution for releases so users can pull typos without building from source or relying on stale third-party images.

Refs: #427
Related: #1116, #1183

[Copilot]

Pull request overview

Adds official Docker Hub publishing to the release pipeline so users can pull a maintained crateci/typos image instead of building from source or relying on third-party images (refs #427).

Changes:

• Document Docker as an installation/usage option in the README.
• Extend the post-release workflow to build per-arch images, then publish a multi-arch manifest with semver + latest tags to Docker Hub.
• Add a CI job to validate the Docker build on amd64 and arm64.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
README.md	Adds Docker pull instructions for the official image.
.github/workflows/post-release.yml	Builds/pushes per-arch images and merges them into a multi-arch, semver-tagged Docker Hub release image.
.github/workflows/ci.yml	Adds a Docker build validation job (amd64 + arm64) as part of CI.

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[Copilot]

This adds an ARM64 Docker build to the PR CI matrix using the ubuntu-24.04-arm runner. That will run on every PR and can significantly increase CI time/cost and may be impacted by ARM runner availability. Consider running the ARM64 Docker build only on push to master/tags (or a scheduled workflow), or building ARM64 via Buildx+QEMU on ubuntu-latest if the goal is just to validate the Dockerfile.

Suggested change

	include:
	- platform: linux/amd64
	runner: ubuntu-latest
	- platform: linux/arm64
	runner: ubuntu-24.04-arm
	runs-on: ${{ matrix.runner }}
	steps:
	- name: Checkout repository
	uses: actions/checkout@v6
	platform: ["linux/amd64", "linux/arm64"]
	runs-on: ubuntu-latest
	steps:
	- name: Checkout repository
	uses: actions/checkout@v6
	- name: Set up QEMU
	uses: docker/setup-qemu-action@v3

[andrey-fomin]

Hi @epage. Which approach do you think makes the most sense here?

• Keep the current setup and use a separate ARM64 runner.
• Skip building the ARM64 Docker image in CI, assuming that a successful AMD64 build makes an ARM64 failure unlikely.
• Use QEMU for ARM64 builds.

[andrey-fomin]

Before enabling this workflow, repo owners will need to:

• create a Docker Hub access token with permission to push to that repository
• add DOCKERHUB_USERNAME as a GitHub Actions variable
• add DOCKERHUB_TOKEN as a GitHub Actions secret

One thing to confirm before merging:

• what is the correct Docker Hub user/org account for the official image?
  I used crateci/typos as a placeholder since Docker Hub account names cannot contain.

For context, I also created andrey-fomin/typos-docker to build Docker images for typos:
https://github.com/andrey-fomin/typos-docker