Custom policy should be added to allow provider url access

[fbricon]

Task content

Any custom inference endpoint, local (via http://host.openshell.internal:11434/v1 - see #2204) or remote should be accessible by calling openshell like

openshell policy update <sandbox> --add-endpoint <inference-url> --binary '**'

the whitelisted binaries might be restricted to specific agent binaries (opencode, claude, curl ...). See https://github.com/NVIDIA/OpenShell-Community/blob/main/sandboxes/base/policy.yaml