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

modules/repos.sh

@@ -467,8 +467,7 @@ _repos_setup_backports() {
 
     local enable_backports=false
     if _confirm "Backports" "Do you want to enable the official Debian Backports repository?\n\n\
-Backports provides newer, selectively updated packages from the next\n\
-Debian testing branch, recompiled to run stably on your current system.\n\n\
+Backports provides newer, selectively updated packages from the next Debian testing branch, recompiled to run stably on your current system.\n
 Answer NO to disable or remove backports if they are currently enabled." 16 70; then
         enable_backports=true
     fi