feat: complete skylanix rebrand and preseed improvements

- Replace yunohost grub theme with skylanix theme
- Update isolinux menu colors to skylanix branding (#4490a5)
- Refactor preseed configuration with improved package management
- Move Firefox Mozilla installation to main preseed
- Consolidate user shell configuration and system setup
- Streamline late custom scripts for AMD and NVIDIA variants

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

files_to_inject/preseeds/late_custom_nvidia.sh

@@ -37,23 +37,10 @@ apt-get update 2>&1 | filter_warn
 # Installer le noyau XanMod
 apt-get install -y linux-xanmod-x64v3 2>&1 | filter_warn
 
+# Installer Kisak Mesa
+apt-get -y dist-upgrade 2>&1 | filter_warn
+
 # Pilotes NVIDIA
 apt-get install -y $(apt-cache search --names-only '^nvidia-driver-[0-9]+$' | sort -V | tail -1 | cut -d' ' -f1) nvidia-settings 2>&1 | filter_warn
 
-# Ajouter flathub à flatpak
-timeout 30 flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo || true
-
-# Supprimer Konqueror si présent
-apt-get remove --purge -y konqueror 2>&1 | filter_warn
-
-# Mettre le shell fish pour chaque utilisateur non root
-for u in $(awk -F: '$3 >= 1000 && $3 < 65534 { print $1 }' /etc/passwd); do
-    chsh -s /usr/bin/fish $u 2>/dev/null || true
-done
-
-# Activer le support i386 et mettre le système à niveau
-dpkg --add-architecture i386 || true
-apt-get update 2>&1 | filter_warn
-apt-get -y dist-upgrade 2>&1 | filter_warn
-
 exit 0