Security hardening & DRY refactoring

- Fixed command injection in desktop_display.sh by converting word-splitting loops to safe array-based iteration for LightDM/GDM3 configuration and XFCE package installation.
- Added symlink detection guard before repository file operations in repos.sh to prevent TOCTOU attacks during restore_previous_repos().
- Hardened SUDO_USER resolution with awk validation against /etc/passwd to prevent root fallback and ensure real login users are targeted for sudoers configuration.
- Implemented algorithm (lz4/zstd) and size validation before ZRAM configuration writes in zram.sh to reject invalid inputs.
- Protected grep MemTotal read from /proc/meminfo with 2>/dev/null and default assignment under set -u.
- Added || true guards around apt-cache madison pipelines in firmware.sh, kernel.sh, gpu.sh, and utils.sh to prevent pipefail aborts when backports unavailable.
- Wrapped whiptail installation in if/else blocks to allow offline error messages instead of script termination under set -e.
- Fixed grep -c output duplication in swap.sh with proper || true pattern and default variable assignment.
- Replaced unquoted $cleaned loops with array conversion using while read for secure package iteration across gaming, desktop_display, firmware, and kernel modules.
- Anchored sed regex patterns to space-delimited "main" components to prevent mirror URL corruption in sources.list editing.
- Escaped % characters in _msg() function before passing to whiptail to prevent printf format interpretation crashes.
- Consolidated package version helpers into canonical wrappers: _get_pkg_version, _get_installed_version, _get_backports_version for consistent apt/dpkg queries.
- Created _install_if_missing() and _install_pkg() with proper error handling that respects set -e while providing user feedback on installation failures.
- Removed 6 dead code functions (~51 lines): check_system_time, sync_system_time, get_cpu_summary, get_ram_summary, pkg_versions, get_backports_kernel_version.
- Added detect_displayserver and detect_audio_server to refresh_system_state() for complete state refresh when returning from menus.
- Enhanced _on_interrupt() trap handler to kill lingering apt/dpkg child processes and clean /tmp/debianito.* temporary files on Ctrl+C or TERM.
- Improved restore_previous_repos() with manifest-based backup verification (.backed_up_* markers) to prevent destructive repository file deletion.
- Added mktemp usage for secure temporary deb file downloads in nvidia.sh, heroic.sh, and tools.sh to eliminate TOCTOU vulnerabilities in /tmp.
- Fixed Bluetooth USB dongle misclassification as WiFi devices by excluding "bluetooth" strings from USB_WIFI_DEVS detection in firmware.sh.
- Properly utilized the need array for selective package installation in internet.sh instead of hardcoding full package list.
- Corrected fwupdmgr duplicate execution and grep false positives in system.sh with strict pattern matching for available updates.
- update docs and added quickstart guide

modules/kernel.sh

@@ -16,18 +16,18 @@ show_kernel_menu() {
         clear
 
         case "$choice" in
-            stable)    _install_kernel_package "linux-image-amd64" "Stable" "" ;;
-            rt)        _install_kernel_package "linux-image-rt-amd64" "RT" "" ;;
-            cloud)     _install_kernel_package "linux-image-cloud-amd64" "Cloud" "" ;;
-            backports)
-                if [ "$(is_backports_enabled)" != "true" ]; then
-                    _msg "Kernel" "Backports repository is not enabled.\n\nUse option 3 (Configure repositories) to enable backports\nbefore installing the backports kernel."
-                else
-                    _install_kernel_package "linux-image-amd64" "Backports" \
-                        "-t ${DEBIAN_CODENAME}-backports"
-                fi
-                ;;
-            back) break ;;
+        stable) _install_kernel_package "linux-image-amd64" "Stable" "" ;;
+        rt) _install_kernel_package "linux-image-rt-amd64" "RT" "" ;;
+        cloud) _install_kernel_package "linux-image-cloud-amd64" "Cloud" "" ;;
+        backports)
+            if [ "$(is_backports_enabled)" != "true" ]; then
+                _msg "Kernel" "Backports repository is not enabled.\n\nUse option 3 (Configure repositories) to enable backports\nbefore installing the backports kernel."
+            else
+                _install_kernel_package "linux-image-amd64" "Backports" \
+                    "-t ${DEBIAN_CODENAME}-backports"
+            fi
+            ;;
+        back) break ;;
         esac
     done
 }
@@ -44,7 +44,8 @@ _install_kernel_package() {
 
     if [ "$flavor" = "Backports" ] && [ "$GPU_TYPE" = "nvidia" ]; then
         if ! _confirm "Kernel" "WARNING: Backports kernel changes the kernel version.\nYour NVIDIA driver will need recompilation (DKMS).\n\nProceed?"; then
-            echo "Skipping."; return
+            echo "Skipping."
+            return
         fi
     fi
     if [ "$flavor" = "RT" ] && [ "$GPU_TYPE" = "nvidia" ]; then
@@ -54,8 +55,8 @@ _install_kernel_package() {
     local headers_pkg="${pkg_base/linux-image-/linux-headers-}"
     local ver headers_ver
     if [ -n "$bpo_flag" ]; then
-        ver=$(apt-cache madison "$pkg_base" 2>/dev/null | grep "${DEBIAN_CODENAME}-backports" | awk '{print $3}' | head -1)
-        headers_ver=$(apt-cache madison "$headers_pkg" 2>/dev/null | grep "${DEBIAN_CODENAME}-backports" | awk '{print $3}' | head -1)
+        ver=$(apt-cache madison "$pkg_base" 2>/dev/null | grep "${DEBIAN_CODENAME}-backports" | awk '{print $3}' | head -1 || true)
+        headers_ver=$(apt-cache madison "$headers_pkg" 2>/dev/null | grep "${DEBIAN_CODENAME}-backports" | awk '{print $3}' | head -1 || true)
     else
         ver=$(apt-cache show "$pkg_base" 2>/dev/null | sed -n 's/^Version: //p' | grep -v '~bpo' | head -1)
         headers_ver=$(apt-cache show "$headers_pkg" 2>/dev/null | sed -n 's/^Version: //p' | grep -v '~bpo' | head -1)
@@ -66,7 +67,8 @@ _install_kernel_package() {
     [ -n "$bpo_flag" ] && summary+="\n  From:    ${DEBIAN_CODENAME^}-backports"
 
     if ! _confirm "Kernel — ${flavor}" "$summary"; then
-        echo "Skipping."; return
+        echo "Skipping."
+        return
     fi
 
     _run_cmd "Kernel" "sudo apt install -y ${bpo_flag} ${pkg_base} ${headers_pkg}" \