Properly enable zsh system-wide when enabled

modules/core/default.nix

@@ -17,5 +17,6 @@
     ./stylix.nix
     ./system.nix
     ./user.nix
+    ./zsh.nix
   ];
 }

modules/core/zsh.nix

@@ -0,0 +1,14 @@
+{
+  config,
+  lib,
+  ...
+}:
+with lib;
+let
+  zshCfg = config.modules.zsh;
+in
+{
+  config = mkIf zshCfg.enable {
+    programs.zsh.enable = true;
+  };
+}