Rename Release workflow to Publish and add public GHCR tags; update README

[remdui]

Motivation

• Clarify and rename the release workflow to Publish to reflect that it publishes images to GHCR.
• Ensure published images include a conditional latest tag and a sha-<commit> tag for traceability.
• Update documentation to describe the public multi-arch publishing behavior and to clarify the release steps.

Description

• Renamed the GitHub Actions workflow name from Release to Publish in .github/workflows/release.yml.
• Updated Docker metadata extraction in the workflow to emit a conditional latest raw tag and a sha-<commit> tag alongside tag/ref/semver outputs.
• Left the build/push and release steps intact while maintaining multi-arch build configuration via PLATFORMS and docker/build-push-action settings.
• Updated README.md to change the badge label to Publish, note that multi-arch images are published publicly to GHCR, add a short paragraph enumerating the tags produced for a version tag, and clarify the ./update_version.sh / push step wording.

Testing

• No automated test runs were executed as part of this change because it only updates CI workflow metadata and documentation.
• The repository CI and publish workflow will run on their respective triggers (e.g., tag pushes) when exercised later; this PR does not include runtime test output.

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Codex Task