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.

flake.nix

@@ -45,6 +45,7 @@
         ./desktop/dev.nix
         ./desktop/office.nix
         ./desktop/gaming.nix
+        ./desktop/media.nix
         ./desktop/virtualization.nix
         ./desktop/crypto.nix
       ];
@@ -77,7 +78,7 @@
       };
       skip01 = mkSystem {
         modules = [
-          ./systems/common.nix
+          ./systems/common-headless.nix
           ./systems/skip01.nix
           ./users/jsutter.nix
           ./servers/common.nix