fix(3167): wire the swarm-ui package from the flake, not a pkgs attr

The option defaulted to pkgs.swarm-ui, which does not exist: this
project has no overlay - flake.nix's nixosModules.default wires package
options with mkDefault from its own package set, and swarm.controller
does exactly that. The default would have failed to evaluate on any real
deployment, not just in a test harness.

Found by the gate forcing .package: the earlier probes passed because
they only read option values that never touched it.

flake.nix

@@ -148,6 +148,9 @@
               services.hyperhive.swarm.controller.swarmctlPackage =
                 lib.mkDefault
                   self.packages.${pkgs.stdenv.hostPlatform.system}.swarmctl;
+              services.hyperhive.swarm.ui.package =
+                lib.mkDefault
+                  self.packages.${pkgs.stdenv.hostPlatform.system}.swarm-ui;
               services.hyperhive.gateway.swaggerUiTheme =
                 lib.mkDefault
                   self.packages.${pkgs.stdenv.hostPlatform.system}.swagger-ui-theme;

nix/host-modules/swarm-ui.nix

@@ -9,7 +9,6 @@
 {
   lib,
   config,
-  pkgs,
   ...
 }:
 let
@@ -57,12 +56,17 @@ in
 
     package = lib.mkOption {
       type = lib.types.package;
-      default = pkgs.swarm-ui;
+      defaultText = lib.literalExpression "hyperhive.packages.\${system}.swarm-ui";
-      defaultText = lib.literalExpression "pkgs.swarm-ui";
       description = ''
         Static build of the swarm UI. nginx serves this store path
         directly — there is no server-side component beyond the
         controller's own API.
+
+        Wired by default from this flake's own package set (see
+        `flake.nix`), the same way `swarm.controller.package` is. There
+        is deliberately **no overlay** in this project, so a
+        `pkgs.swarm-ui` default here would name an attribute that does
+        not exist on any real deployment.
       '';
     };
   };