Add Zero-OS customization before CPIO creation

- Add initramfs_finalize_customization() function
- Remove root password for passwordless login (sed -i 's/^root:[^:]*:/root::/' /etc/passwd)
- Update /etc/motd and /etc/issue to Zero-OS branding instead of Alpine
- Called automatically before CPIO creation
- Fixes init script duplication issue (/init vs /sbin/init)
- Correct boot flow: /init → switch_root → /sbin/zinit init (no /sbin/init needed)

config/init

@@ -112,6 +112,6 @@ fi
 
 echo "[+] switching root"
 echo "  exec switch_root /mnt/root /sbin/zinit init"
-exec switch_root /mnt/root /sbin/zinit init
+exec switch_root /mnt/root /sbin/zinit -d init
 
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