feat(nixos): add AdGuard to Homepage

configs/nixos/guests/adguard.nix

@@ -13,6 +13,22 @@ in
   };
 
   config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = cfg.address != null;
+        message = "guests.adguard.address must identify the AdGuard Home guest.";
+      }
+    ];
+
+    registry.homepage.${config.networking.hostName}.adguard = {
+      tab = "System";
+      section = "Network";
+      name = "AdGuard Home";
+      description = "Blocks advertisements and trackers.";
+      icon = "adguard-home.svg";
+      href = "http://${cfg.address}";
+    };
+
     guests.adguard = {
       interior.modules.services.adguardhome = {
         enable = true;