verbena: configure IPv6 from tofu outputs

machines/verbena/configuration.nix

@@ -1,4 +1,7 @@
 { self, lib, ... }:
+let
+  tf_outputs = builtins.fromJSON (builtins.readFile ../../infra/outputs.json);
+in
 {
   imports = [
     self.nixosModules.nix-defaults
@@ -16,6 +19,19 @@
 
   networking.useDHCP = lib.mkDefault true;
 
+  networking.defaultGateway6 = {
+    address = tf_outputs.verbena_gateway6.value;
+    interface = "ens3";
+  };
+  networking.interfaces."ens3" = {
+    ipv6.addresses = [
+      {
+        address = tf_outputs.verbena_ipv6.value;
+        prefixLength = 64;
+      }
+    ];
+  };
+
   clan.core.settings.state-version.enable = true;
 
   services.nginx = {