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/kernel.sh

@@ -4,7 +4,7 @@
 show_kernel_menu() {
     while true; do
         local items=("stable" "Install linux-image-amd64")
-        [ "$DEBIAN_VERSION" != "11" ] && items+=("backports" "Install from backports")
+        [ "$DEBIAN_VERSION" = "13" ] && items+=("backports" "Install from backports")
         items+=("rt" "Install linux-image-rt-amd64 (Preempt-RT)")
         items+=("cloud" "Install linux-image-cloud-amd64")
         items+=("back" "Return to main menu")