fix(scripts): fix shared.sh guard logic and echo -e portability

- shared.sh: simplify guard logic, remove misleading warning message,
  use ${VAR:-} pattern to avoid unbound variable error
- install-cheat-purebashbible.sh: replace echo -e with printf for
  POSIX portability

scripts/shared.sh

@@ -4,17 +4,8 @@
 # Helper env variables. Use like this: VERBOSE=1 ./script.sh
 : "${VERBOSE:=0}"
 
-# Set variable that checks if the shared.sh script has been
-# sourced only once If the script has been sourced more than once,
-# the script not be sourced again.
-[ -z "$SHARED_SCRIPTS_SOURCED" ] && {
-
+# Source the main shared config if not already loaded
+if [ -z "${SHARED_SCRIPTS_SOURCED:-}" ]; then
   source "${DOTFILES}/config/shared.sh"
-  # Warn the user if the shared configuration hasn't been loaded yet
-  msgr warn "(!) shared.sh not sourced"
-
-  # Set variable that checks if the shared.sh script has been
-  # sourced only once.
-  # shellcheck disable=SC2034
   export SHARED_SCRIPTS_SOURCED=1
-}
+fi