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/gaming.sh

@@ -40,7 +40,10 @@ ensure_contrib_repo() {
         fi
     else
         if [ -f /etc/apt/sources.list ]; then
-            sudo sed -i '/^deb / { /contrib/! s/main/main contrib/ }' /etc/apt/sources.list
+            sudo cp /etc/apt/sources.list "/etc/apt/sources.list.backup.$(date +%Y%m%d_%H%M%S)"
+            # Anchor to the space-delimited "main" component so mirror URLs
+            # containing "main" (e.g. https://main.example.com) are untouched.
+            sudo sed -i -E '/^deb / { /\bcontrib\b/! s/ main([[:space:]]|$)/ main contrib\1/ }' /etc/apt/sources.list
         fi
         if [ -d /etc/apt/sources.list.d ]; then
             for f in /etc/apt/sources.list.d/*.sources; do
@@ -94,15 +97,23 @@ install_gaming() {
 
     # 2. Determine if 32-bit is needed (steam, lutris, or explicit i386 toggle)
     local need_32bit=false
-    for p in $cleaned; do
-        case $p in steam | lutris) need_32bit=true ;; esac
+
+    local -a install_pkgs=()
+    while IFS= read -r _pkg; do
+        [ -n "$_pkg" ] && install_pkgs+=("$_pkg")
+    done < <(echo "$cleaned" | tr ' ' '\n')
+
+    for p in "${install_pkgs[@]}"; do
+        case "$p" in steam | lutris) need_32bit=true ;; esac
     done
     echo "$cleaned" | grep -qw i386 && need_32bit=true
 
     # Strip pseudo-entry "i386" from the install list
-    local install_list
-    install_list=$(echo "$cleaned" | tr ' ' '\n' | grep -v '^i386$' | tr '\n' ' ')
-    install_list=${install_list% }
+    local -a install_list=()
+    while IFS= read -r _pkg; do
+        [ "$_pkg" = "i386" ] && continue
+        [ -n "$_pkg" ] && install_list+=("$_pkg")
+    done < <(echo "$cleaned" | tr ' ' '\n')
 
     # 3. Enable i386 architecture if needed
     if $need_32bit && ! dpkg --print-foreign-architectures 2>/dev/null | grep -q i386; then
@@ -122,7 +133,7 @@ install_gaming() {
     fi
 
     # 5. Install selected packages
-    for pkg in $install_list; do
+    for pkg in "${install_list[@]}"; do
         case $pkg in
         steam)
             if ensure_contrib_repo; then