System-Wide Refactor & Critical Fixes

- Resolved NVIDIA driver management issues by expanding package detection patterns (including nvidia-open and nvidia-kernel-open-dkms), enhancing purge process to ensure clean uninstallation of v590/595 drivers, and adding conditional skip for manage menu when no driver is installed.  
- Enhanced Firefox variant selection in internet.sh using exact token matching (grep -qx) instead of substring search to prevent incorrect removal or unintended ESR/Firefox conflicts. 
- New XFCE install option with 4 options
- Restructured Desktop Environment into two-level menu system with dispatcher and Xfce sub-menu for scalability, enabling future additions like GNOME/KDE without disrupting existing flows.  
- Added Polkit rules in desktop_display.sh to grant suspend permissions without password prompts on laptops, including idempotent group (backlight) creation and user membership management with || true fallbacks.  
- Enforced LC_ALL=C LANGUAGE=C environment variables for all dpkg-reconfigure commands across System Preferences and utils.sh to ensure native dialogues run consistently in English.  
- Fixed kernel backports menu option availability to only appear on Debian 13, preventing errors on Debian 12 where backports repositories are EOL.  
- Improved ZRAM module initialization sequence by ensuring swapoff and zram module removal occur before writing new configuration files to prevent race conditions during system setup.

modules/gpu.sh

@@ -191,12 +191,19 @@ _install_nvidia_stack() {
 
     NVIDIA_DRIVER_MODE=""
 
-    if ! _nvidia_manage_menu; then
-        return
+    if _nvidia_driver_installed; then
+        if ! _nvidia_manage_menu; then
+            return
+        fi
     fi
 
     if [ "$DEBIAN_VERSION" = "11" ]; then
-        install_nvidia_bullseye
+        if type install_nvidia_bullseye &>/dev/null; then
+            install_nvidia_bullseye
+        else
+            _msg "NVIDIA — Bullseye" "The Bullseye NVIDIA module is not available.\n\nNo NVIDIA driver was installed." 10 60
+            NVIDIA_DRIVER_MODE=""
+        fi
 
     else
         if ! _show_nvidia_version_menu; then
@@ -230,7 +237,9 @@ _install_nvidia_stack() {
                         NVIDIA_DRIVER_MODE=""
                         ;;
                     blackwell)
-                        _install_nvidia_cuda_repo
+                        _msg "NVIDIA — Blackwell (v550)" \
+                            "Your Blackwell GPU is NOT supported by the official\nDebian v550 driver.\n\nPlease select v590 or v595 (NVIDIA CUDA Repo)\nin the driver menu." 14 65
+                        NVIDIA_DRIVER_MODE=""
                         ;;
                     maxwell|pascal|volta)
                         if [ "$(is_backports_kernel)" = "true" ]; then
@@ -253,7 +262,7 @@ Forcing the stable driver path." 14 70
                             _install_nvidia_standard
                         fi
                         ;;
-                    turing|ampere|ada|blackwell)
+                    turing|ampere|ada)
                         _install_nvidia_standard
                         ;;
                     *)