v0.48.0

`docker-image-workflow.yml` now keeps build caches stable across main, tags, and retries. Multi-image callers can also provide separate registry cache refs for oversized variants.

- The default GitHub Actions cache scope now derives from the caller repository and image variant instead of the current ref.
- A multi-image target may set `cache_from` and `cache_to`. This lets a large CPU or CUDA build use its own max-mode registry cache without competing for the caller's GitHub Actions cache budget.