gitea act_runner exposes GITHUB_* not GITEA_* variable aliases;
switch to GITHUB_REF_NAME and GITHUB_OUTPUT so tag extraction works.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Add Gitea Actions workflows (ci.yml, release.yml) that build and push
to registry.ginnoir.com. Disable GitHub release creation. Update all
doc/compose references from ghcr.io to registry.ginnoir.com.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>