servo-vpn: resolve DNS through the VPN

hosts/common/vpn.nix

@@ -38,7 +38,9 @@ let
     endpoint = config.sane.hosts.by-name."servo".wg-home.endpoint;
     publicKey = config.sane.hosts.by-name."servo".wg-home.pubkey;
     address = [ config.sane.services.wg-home.ip ];
-    dns = [ "10.78.79.1" ];
+    dns = [
+      config.sane.hosts.by-name."servo".wg-home.ip
+    ];
     privateKeyFile = config.networking.wireguard.interfaces.wg-home.privateKeyFile;
     extraOptions = {
       # wg-home and vpn-servo interfaces interfere with the result that when connected to both,

hosts/modules/wg-home.nix

@@ -83,6 +83,7 @@ in
       {
         listenPort = 51820;
         privateKeyFile = "/run/wg-home.priv";
+        # TODO: this make this `wants` and `after`, instead of manually starting it
         preSetup =
           let
             gen-key = config.sane.fs."/run/wg-home.priv".unit;