BraveActivity shows LinkVpnSubscriptionDialogFragment when a VPN subscription is detected on the device and the link dialog has not yet been shown. The guard did not consult the VPN policy pref, so the dialog was presented even to users whose VPN has been disabled by policy (e.g. Brave Origin users with VPN turned off at the policy layer). Add !BraveVpnPolicy.isDisabledByPolicy(mTabModelProfileSupplier.get()) to the guard. Resolves: https://github.com/brave/brave-browser/issues/54786