Refresh wallpapers and update configs

- Set default stylix wallpaper to “The‑Southern‑Raiders.jpg” and comment
  out the old image.
- Bump helium AppImage to version 0.12.1.1 with updated URL and
  checksum.
- Switch NVIDIA driver package from beta to stable.
- Change “kys” alias to use systemctl poweroff and add “jezus” alias for
  reboot.

modules/drivers/nvidia-drivers.nix

@@ -36,7 +36,7 @@ in {
         # accessible via `nvidia-settings`.
         nvidiaSettings = true;
         # Optionally, you may need to select the appropriate driver version for your specific GPU.
-        package = config.boot.kernelPackages.nvidiaPackages.beta;
+        package = config.boot.kernelPackages.nvidiaPackages.stable;
       };
     };
   };