amd gcn legacy support & kernel overhaul

- Fixed Mesa 32-bit dependency conflicts by removing mesa-va-drivers from gaming setup; mesa-libgallium now includes VA-API for Mesa >= 25.3.3, resolving solver errors with backports (Mesa 26.x).
- Removed corectrl detection and installation from AMD tools in gpu/amd_intel.sh (retained in System Tools checklist only).
- Added zutty terminal emulator option alongside alacritty for Debian 12+ in terminals.sh.
- Overhauled Kernel menu: replaced "Backports Kernel" with "Kernel" submenu offering Stable, RT, Cloud, and Backports options; removed hardcoded Debian 11 restriction (backports hidden only on Bullseye); headers now installed automatically with all kernel variants; NVIDIA warnings added for Backports (DKMS required) and RT (driver compatibility note).
- Implemented AMD GCN legacy driver migration: is_amd_legacy_gcn() function detects GCN 1.0/1.1 GPUs via whitelist of 85 PCI IDs; offers user prompt to force amdgpu module with GRUB parameters (radeon.si_support=0, radeon.cik_support=0, amdgpu.si_support=1, amdgpu.cik_support=1); safe sed-based injection into GRUB_CMDLINE_LINUX_DEFAULT with backup and idempotency check.
- Standardized UI across 27 checklist locations: unified text to "Check [*] the packages you want installed/updated on your system."; removed SCROLL_HINT variable entirely from all code; changed OK button to "Apply" in _checklist() and _inputbox() only (not in _msg/_menu).
- Reordered gaming menu checklists: i386 moved to top position, steam/mangohud positioned immediately after for better dependency flow.
- Enhanced kernel installation prompts: all variants (Stable, RT, Cloud, Backports) now display candidate version numbers in parentheses using apt-cache policy and madison queries.
- update readme

debianito.sh

@@ -62,7 +62,7 @@ main_menu() {
             "3" "Configure Repositories" \
             "4" "Firmware, Wireless & Bluetooth" \
             "5" "Graphics Drivers & Mesa Stack" \
-            "6" "Backports Kernel" \
+            "6" "Kernel" \
             "7" "Gaming Setup" \
             "8" "ZRAM" \
             "9" "Swap Management" \
@@ -104,15 +104,7 @@ main_menu() {
                 esac
                 STATE_REFRESHED=true
                 ;;
-            6)
-                if [ "$DEBIAN_VERSION" = "11" ]; then
-                    _msg "Not Available" \
-                        "Backports Kernel is not available on Debian 11 Bullseye.\n\nThe stable kernel provided by Bullseye is the only option." 10 60
-                else
-                    install_kernel_backports || true
-                fi
-                STATE_REFRESHED=true
-                ;;
+            6)  show_kernel_menu || true ;;
             7)
                 if [ "$DEBIAN_VERSION" = "11" ] && type install_gaming_bullseye &>/dev/null; then
                     install_gaming_bullseye || true