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

README.md

@@ -87,6 +87,18 @@ The submenu offers the next categories:
 
 ---
 
+## Quick Start Guide
+
+For a streamlined post-installation setup (~15-20 minutes), refer to the [Quick Start Visual Guide](/docs/quickstart.md). It provides:
+
+- Step-by-step recommended order for running Debianito options (Steps 1–13)
+- What each option does and when to enable it
+- Screenshots of key dialogs (whiptail menus, confirmations, hardware detection)
+- Troubleshooting tips for common issues (WiFi after firmware install, NVIDIA + Wayland, GRUB boot menu hidden, etc.)
+
+**Tip:** If you're unsure where to start, follow Steps 1–5 from the Quick Start guide. They cover the essentials: system info, permissions, repositories, firmware, and graphics drivers.
+
+---
 ## File Structure
 
 | Directory/File | Description |
@@ -110,7 +122,7 @@ The submenu offers the next categories:
 │   ├── gaming.md
 │   ├── gpu.md
 │   ├── kernel.md
-│   ├── QUICKSTART.md
+│   ├── quickstart.md
 │   ├── repos_config.md
 │   ├── retroarch.md
 │   ├── swap.md
@@ -119,8 +131,25 @@ The submenu offers the next categories:
 │   ├── user_priv_feed.md
 │   └── zram.md
 ├── media
-│   └── gift
-│       └── script.gif
+│   ├── gift
+│   │   └── script.gif
+│   └── screenshots
+│       ├── 01-system-info.png
+│       ├── 02b-pwfeedback.png
+│       ├── 02-user-privileges.png
+│       ├── 03-system-prefs.png
+│       ├── 04b-backports.png
+│       ├── 04-repos.png
+│       ├── 05-firmware-plan.png
+│       ├── 06-gpu-choice.png
+│       ├── 07-kernel.png
+│       ├── 08-gaming.png
+│       ├── 09b-zram-status.png
+│       ├── 09-zram-algo.png
+│       ├── 10b-swap-status.png
+│       ├── 10-swap.png
+│       ├── 11b-essential-pack.png
+│       └── 11-programs.gif
 ├── modules
 │   ├── bluetooth.sh
 │   ├── bullseye