fix(iso): fix memtest86+ path (bookworm uses memtest86+x64.bin/.efi)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/config/bootloaders/grub-pc/grub.cfg

@@ -29,9 +29,15 @@ menuentry "EASY-BEE (fail-safe)" {
     initrd  @INITRD_LIVE@
 }
 
-menuentry "Memory Test (memtest86+)" {
-    linux16 /boot/memtest86+.bin
-}
+if [ "${grub_platform}" = "efi" ]; then
+    menuentry "Memory Test (memtest86+)" {
+        chainloader /boot/memtest86+x64.efi
+    }
+else
+    menuentry "Memory Test (memtest86+)" {
+        linux16 /boot/memtest86+x64.bin
+    }
+fi
 
 if [ "${grub_platform}" = "efi" ]; then
     menuentry "UEFI Firmware Settings" {