fix backports and system modules

- Refactored `is_backports_enabled()` to dynamically detect backports using `DEBIAN_CODENAME` instead of hardcoded strings, improving script portability.
- Added support for standalone classic backports files (`/etc/apt/sources.list.d/debian-backports.list`) and deb822 format (`*.sources`) to ensure consistent detection across different repository configurations.
- Resolved Mesa and Kernel backports detection bugs, ensuring correct dialogue prompts and preventing false error messages during installation.
- Implemented smart rounding for zram memory allocation to the nearest Gigabyte for optimized performance.
- Enhanced Whiptail manual input validation for zram to block empty, non-numeric, or zero values.
- Introduced a dedicated `software_centers.sh` module for the modular and clean installation of GNOME Software and Plasma Discover.
- Added smart desktop environment detection (GTK/QT) to automatically suggest and install the optimal software center.
- Implemented a two-phase installation flow for software centers (Base Store -> Optional Flatpak support) with static consistency warnings based on the detected desktop environment.
- update README.md

modules/extras.sh

@@ -38,9 +38,10 @@ install_extras() {
             "6" "Code Editors & IDEs" \
             "7" "Servers & Dev Tools" \
             "8" "Security & Networking" \
-            "9" "System Tools" \
-            "10" "Fetch / System Info" \
-            "11" "Back to main menu" \
+            "9" "Software Centers" \
+            "10" "System Tools" \
+            "11" "Fetch / System Info" \
+            "12" "Back to main menu" \
             3>&1 1>&2 2>&3)
 
         [ -z "$cat_choice" ] && return
@@ -56,9 +57,10 @@ install_extras() {
             6)  _cat_programming ;;
             7)  _cat_dev ;;
             8)  _cat_security ;;
-            9)  _cat_general ;;
-            10) _cat_fetch ;;
-            11) return ;;
+            9)  _cat_software_centers ;;
+            10) _cat_general ;;
+            11) _cat_fetch ;;
+            12) return ;;
         esac
         clear
     done