fix(install): use $EUID builtin for root detection

Replace $(id -u) with ${EUID:-$(id -u)} for more reliable root
detection in bash, falling back to id -u if EUID is not set.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: ebadenes

install.sh

@@ -52,7 +52,7 @@ if [ -z "$unzip_tool" ]; then
 fi
 
 # Determine install directory based on whether we are root or not
-if [ "$(id -u)" -ne 0 ]; then
+if [ "${EUID:-$(id -u)}" -ne 0 ]; then
     printf "\nYou are not running as root.\n"
     printf "Install eclone to ~/.local/bin instead of /usr/bin? [Y/n] "
     read -r answer </dev/tty