refactor: no group list in an account's details, and no Microsoft Graph call for it

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/provider/provider.go

@@ -227,10 +227,3 @@ func (d *Denied) Unwrap() error { return d.Err }
 type ContainerDetails interface {
 	Details(ctx context.Context, c Container) ([]Attr, error)
 }
-
-// AccountGroups is implemented by providers that can list the groups
-// their account is a member of, directly or through other groups. It
-// goes over the network.
-type AccountGroups interface {
-	Groups(ctx context.Context) ([]string, error)
-}