Move Modrinth App to a shared package

homes/career/desktop/default.nix

···
 
     (import ./firefox.nix { inherit homeDesktop; })
 
+    (flakeRoot + /homes/shared/desktop/modrinth.nix)
     (flakeRoot + /homes/shared/desktop/prismlauncher.nix)
 
     ./packages.nix

homes/career/desktop/packages.nix

···
   home.packages = with pkgs; [
     slack
     notion-app-enhanced
-
-    # Awaiting the merge of #466573
-    #modrinth-app
   ];
 }

homes/shared/desktop/modrinth.nix

···
+{ pkgs-unstable, ... }:
+
+{
+  home.packages = with pkgs-unstable; [
+    modrinth-app
+  ];
+}