## Describe your changes
A group could be deleted while a reverse proxy service still referenced
it, silently breaking the service's access control: private services
list groups in `access_groups` as the peer allowlist, and SSO bearer
auth distributes tokens to `distribution_groups`.
Group deletion now runs through the same linkage validation as routes,
policies, and agent network policies: deleting a group that backs a
private service allowlist or an enabled bearer-auth distribution list
fails with a `GroupLinkError` naming the service domain. Disabled bearer
configs and stale `access_groups` on non-private services are inert and
do not block deletion.
Tests cover both linked cases in single and bulk deletion, and pin the
non-blocking cases. The test account seeds decoy services ahead of the
linked ones so the check is proven to scan the full service list.
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