Refactor NixOS configuration: Move GUI apps to desktop modules and create headless config

- Move GUI applications from users/jsutter.nix to appropriate desktop modules:
  * office.nix: slack, signal-desktop
  * gaming.nix: discord, stremio
  * plasma.nix: arc-theme, pinentry, tigervnc
  * dev.nix: putty
  * media.nix (new): vlc, deluge

- Create systems/common-headless.nix for server configurations:
  * Remove GUI dependencies (Flatpak, XDG portals, fonts, graphics drivers)
  * Include only essential CLI tools and server packages
  * Disable X server completely

- Simplify skip01 configuration:
  * Remove Intel graphics drivers and OpenGL support
  * Use headless common configuration
  * Keep unified users/jsutter.nix (no split files)

- Update flake.nix to include new media.nix module in desktop systems

Result: Clean separation between desktop and headless configurations
with improved modularity and maintainability.

desktop/office.nix

@@ -1,12 +1,12 @@
-{ config, pkgs, ... }:
+{ config, pkgs, pkgs-unstable, ... }:
 
 {
-
-
-environment.systemPackages = with pkgs; [
-  libreoffice-qt
-  thunderbird
-#  gimp  # Temporarily commented out to avoid build errors
-#  calibre
+  environment.systemPackages = with pkgs; [
+    libreoffice-qt
+    thunderbird
+    slack                        # Team communication
+    pkgs-unstable.signal-desktop # Private messaging
+#   gimp  # Temporarily commented out to avoid build errors
+#   calibre
   ];
 }