Add GHCR publish workflow for Docker image builds

[Copilot]

This change adds CI automation to build the repository Docker image and publish it to GitHub Packages (GHCR). It introduces a dedicated workflow for both continuous publishing from main and release-oriented publishing from version tags.

• Workflow: container publish pipeline

  • Added .github/workflows/docker-publish.yml.
  • Triggers on:
    • pushes to main
    • version tags matching v*
    • manual workflow_dispatch

• Registry publishing setup

  • Uses GITHUB_TOKEN with packages: write permission to authenticate to ghcr.io.
  • Publishes image under ghcr.io/${{ github.repository }}.

• Build and tag strategy

  • Uses docker/metadata-action to generate tags and labels.
  • Publishes:
    • latest on default branch
    • branch ref tags
    • git tag refs
    • commit SHA tags

- name: Extract Docker metadata
  id: meta
  uses: docker/metadata-action@v5
  with:
    images: ghcr.io/${{ github.repository }}
    tags: |
      type=raw,value=latest,enable={{is_default_branch}}
      type=ref,event=branch
      type=ref,event=tag
      type=sha