Pushes :edge for main and :x.y.z, :x.y and :latest for release tags,
optionally mirrored to another registry. The release workflow no longer
builds the image itself, so a tag does not publish it twice. The README
covers running the image anywhere and the settings the workflows read.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
