feat: Add Secure Boot Support and Remove Grub Entry for Test this Media (#28)

* chore: First pass of adding secure boot key enrollment

* feat: Add secure boot support

* feat: Removed Test this media grub entry and set default to install

* fix: simplify secureboot scripts

---------

Co-authored-by: Kyle Gospodnetich <me@kylegospodneti.ch>

scripts/enroll-secureboot-key.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+set -oue pipefail
+
+readonly SECUREBOOT_KEY="/run/install/repo/ublue-os-akmods-public-key.der"
+readonly ENROLLMENT_PASSWORD="ublue-os"
+
+if [[ ! -d "/sys/firmware/efi" ]]; then
+	echo "EFI mode not detected. Skipping key enrollment."
+	exit 0
+fi
+
+if [[ ! -f "${SECUREBOOT_KEY}" ]]; then
+	echo "Secure boot key not found: ${SECUREBOOT_KEY}"
+	exit 1
+fi
+
+mokutil --timeout -1 || :
+echo -e "${ENROLLMENT_PASSWORD}\n${ENROLLMENT_PASSWORD}" | mokutil --import "${SECUREBOOT_KEY}" || :