fix: expand busybox applet symlinks for init script requirements

Add missing applets used by init scripts: printf, readlink, test, true,
false, which, free, pidof, insmod, modprobe, lsmod, ifconfig, ip, route,
uptime, lsblk, zcat, gunzip, gzip, xz, unxz, du, df, id, ash, halt.

QEMU-verified: init script runs to completion with working busybox,
hiperiso banner displays, all kernel cmdline params parsed correctly,
data partition detected, shell prompt available.

scripts/build_initramfs.sh

@@ -40,7 +40,7 @@ BUSYBOX="${BUSYBOX:-$STAGING/busybox}"
 if [ -x "$BUSYBOX" ]; then
     install -m0755 "$BUSYBOX" "$ROOT/bin/busybox"
     # Create common applet symlinks
-    for app in sh mount umount ls cat echo mkdir mkfifo poweroff reboot sync sleep ln cp mv rm switch_root date grep cut sed awk head tail tr wc basename dirname find mktemp dd mknod losetup blkid dmesg ps kill chmod chown env uname stat tar; do
+    for app in sh ash mount umount ls cat echo printf mkdir mkfifo poweroff reboot halt sync sleep ln cp mv rm switch_root date grep cut sed awk head tail tr wc basename dirname find mktemp dd mknod losetup blkid lsblk dmesg ps kill chmod chown env uname stat tar test true false which readlink free pidof renice insmod modprobe lsmod ifconfig ip route uptime fdisk zcat gunzip gzip xz unxz du df id; do
         ln -sf busybox "$ROOT/bin/$app"
     done
     echo "  [ok] busybox installed"