refactor(nix): Properly modularize home-manager

REF: https://nixos-and-flakes.thiscute.world/nixos-with-flakes/modularize-the-configuration

.config/nix/users/ziro/darwin.nix

@@ -2,6 +2,10 @@
 
 {
   home.homeDirectory = "/Users/ziro";
+  home.packages = lib.mkAfter
+    [
+      pkgs.casks.vscodium
+    ];
 
   programs.browserpass = {
     enable = true;

.config/nix/users/ziro/default.nix

@@ -6,8 +6,6 @@
     packages =
       [
         pkgs.passff-host
-      ] ++ pkgs.lib.optionals (pkgs.stdenv.isDarwin) [
-        pkgs.casks.vscodium
       ];
   };