Multi-platform builds create a manifest index pointing to per-platform
images. The existing labels parameter only sets labels on per-platform
image configs, but GHCR reads annotations from the manifest index for
repository auto-linking. Add index-level annotations so the package
appears under the repo Packages tab instead of only the user profile.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>