fix: remove systemd-boot to resolve build conflict

systemd-boot and GRUB EFI conflict during package configuration.
systemd-boot also fails to configure in chroot (no efivars available).
Using GRUB with shim-signed for UEFI Secure Boot instead.

Changes:
- config/package-lists: Remove systemd-boot, systemd-boot-efi
- tests/unit/secureboot_test.bats: Update test for GRUB instead

Reference: Build failure in binary phase

💘 Generated with Crush

Assisted-by: GLM-5 via Crush <crush@charm.land>

config/package-lists/knel-football.list.chroot

@@ -10,8 +10,6 @@ grub-efi-amd64-bin
 efibootmgr
 efitools
 sbsigntool
-systemd-boot
-systemd-boot-efi
 binutils
 
 # Desktop environment

tests/unit/secureboot_test.bats

@@ -251,8 +251,8 @@
     grep -q "sbsigntool" /workspace/config/package-lists/knel-football.list.chroot
 }
 
-@test "package list includes systemd-boot" {
-    grep -q "systemd-boot" /workspace/config/package-lists/knel-football.list.chroot
+@test "package list includes grub-efi-amd64-signed for Secure Boot" {
+    grep -q "grub-efi-amd64-signed" /workspace/config/package-lists/knel-football.list.chroot
 }
 
 @test "package list includes binutils for objcopy" {