completely refactor and modularize flake

modules/default/common/desktop/applications.nix

@@ -0,0 +1,39 @@
+{ lib, config, pkgs, attrs, system, ... }:
+lib.mkIf config.desktop.enable {
+
+  environment.systemPackages =
+    (with pkgs; [
+
+      bc
+      jq
+      xorg.xrandr
+
+      feh
+
+      enpass
+      vesktop
+      obsidian
+      kicad
+      protonmail-desktop
+      signal-desktop
+
+      piper
+
+      qemu
+
+      libreoffice
+      blender
+      gimp
+      inkscape
+      prusa-slicer
+      UVtools
+      audacity
+
+      glib
+    ])
+    ++
+    [
+      attrs.zen.packages.${system}.specific
+    ];
+
+}