GHCR repos are now public and no longer require authentication by
default. Remove the baked-in XOR-encoded PAT and all automatic
credential injection. Image pulls are unauthenticated unless the user
explicitly provides credentials via --registry-username/--registry-token
flags or OPENSHELL_REGISTRY_USERNAME/OPENSHELL_REGISTRY_TOKEN env vars.
Also adds a new --registry-username CLI flag on gateway start for
private registry use cases, and removes the automatic community
registry credential injection (COMMUNITY_REGISTRY_* env vars) since
community sandbox images on GHCR are also public.
* feat(sandbox): add gpu sandbox scheduling support
Allow sandbox creation to request GPU resources explicitly or infer them from GPU image names. This wires GPU intent through bootstrap, validates gateway support, and adds dedicated GPU E2E coverage for follow-up cluster testing.
Drew Newberry