nvidia & zram fixes

- Fixed critical NVIDIA driver bug on Debian 13 (Trixie) where repo configuration installed v550 instead of selected v595. Implemented version-specific enabling: cuda-keyring for Trixie, extrepo for Bookworm. Added explicit apt update after repo enable and candidate verification before pinning checks to abort cleanly if expected driver unavailable.
- Rewrote `_install_nvidia_standard()` with auto-detected architecture via `_get_nvidia_arch_family()`. Turing/Ampere/Ada/Blackwell → nvidia-open-kernel-dkms (open module); Maxwell/Pascal/Volta/unknown/empty → nvidia-kernel-dkms (closed, safe fallback). Removed all `nvidia-detect` references across modules and docs.
- Fixed `_install_nvidia_cuda_repo()` to use correct CUDA repository package names: v590/v595 → nvidia-open metapackage (includes nvidia-kernel-open-dkms); v550 and below → nvidia-driver. Added dynamic warning message based on installed module type.
- Fixed uninitialized variable bug in `modules/gaming/tools.sh` causing script abortion under `set -u`. Initialized all local variables (`deb_url`, `sha256`, `json`, `deb_suffix`) with default values and added defensive initialization for `$USER` environment variable.
- Fixed ZRAM configuration persistence bug where old config persisted after changes. Added device reset sequence (swapoff + modprobe -r) before writing new config, post-config verification check, and changed default recommendation from 50% to 25% for systems with >16GB RAM.
- Added `_warn_nvidia_gnome_wayland()` function in `gpu.sh` to warn about Debian bug #1109409 (GDM3 + NVIDIA + Wayland black screen issue). Warning displays only when gdm3 present, GNOME Shell 4.x detected, and NVIDIA driver installed.
- Standardized menu headers across all modules using centralized SCROLL_HINT variable, replacing hardcoded strings with uniform Whiptail instructions. Updated documentation for cuda-keyring (Trixie) and ZRAM configuration flow diagrams.

modules/gaming/tools.sh

@@ -26,7 +26,7 @@ install_lutris() {
 }
 
 install_openrgb() {
-    local deb_suffix
+    local deb_suffix=""
     case "$DEBIAN_CODENAME" in
         bookworm) deb_suffix="bookworm" ;;
         trixie)   deb_suffix="trixie" ;;
@@ -41,14 +41,14 @@ install_openrgb() {
 
     _run_cmd "OpenRGB" "sudo apt install -y curl jq" "Installing dependencies..."
 
-    local json
+    local json=""
     json=$(curl -s --connect-timeout 10 \
         "https://codeberg.org/api/v1/repos/OpenRGB/OpenRGB/releases?limit=1") || {
         echo -e "${RED}Could not fetch OpenRGB releases from Codeberg API.${NC}"
         return 1
     }
 
-    local deb_url sha256
+    local deb_url="" sha256=""
     while IFS=' ' read -r url hash; do
         deb_url="$url"
         sha256="$hash"
@@ -87,7 +87,7 @@ install_openrgb() {
     if ! grep -q "^i2c-dev" /etc/modules 2>/dev/null; then
         echo "i2c-dev" | sudo tee -a /etc/modules >/dev/null
     fi
-    sudo usermod -aG i2c "$USER"
+    sudo usermod -aG i2c "${USER:-}"
     sudo udevadm control --reload-rules && sudo udevadm trigger
     sudo setcap cap_sys_rawio=ep /usr/bin/openrgb 2>/dev/null || true