Docker Hub API changes may break Extension updates (in future)

Docker Hub changed their API (per docker/hub-feedback/issues/2484), which removes the current access pathway to the image architecture information. I believe we will[^1] just need to authenticate to fix this one (which is at least possible in a centralised way, unlike with [core updates](https://github.com/bluerobotics/BlueOS/issues/3489)), but in the meantime we have a broken manifest and the CI system will continue to break it (generating it with no images).

Initially raised in [this forum post](https://discuss.bluerobotics.com/t/cant-install-or-update-any-extensions-on-blueboat/21319).

[^1]: once Docker Hub add the info back to the authenticated version of the API, which they have [already said they'll do](https://github.com/docker/hub-feedback/issues/2484#issuecomment-3175459287)

Start by tracing the manifest-generation path and the CI system that queries Docker Hub for image architecture information. Review Docker Hub issue 2484 and the linked forum report to understand the authenticated API behavior. Done means the generated manifest contains the expected images and the CI check no longer breaks when Docker Hub’s access pathway changes.

Written by the indexing model from the issue text.