chore: organise modules

Organise modules in a significantly better way with categories.

modules/applications/default.nix

@@ -0,0 +1,23 @@
+{ config, lib, pkgs, ... }:
+
+{
+  environment.systemPackages = with pkgs; [
+    spotify
+    gimp
+    audacity
+    obsidian
+    keepassxc
+    ani-cli
+  ] ++ lib.optionals pkgs.stdenv.isLinux (with pkgs; [  
+    mpv
+    ghostty
+    thunderbird
+    krita
+    openutau
+    obs-studio
+    blender
+  ]) ++ lib.optionals pkgs.stdenv.isDarwin (with pkgs; [
+    iina
+    utm
+  ]);
+}