Refine exit code to 64 with gnu-getopt note

- Set exit code to 64 per sysexits.h for clarity.
- Added comment on gnu-getopt handling.

Aligns with Unix standards and enhances readability.

Author: Michael Saki

setup-env

@@ -165,8 +165,9 @@ while true; do
       break
       ;;
     *)
+      # Unreachable due to gnu-getopt handling all options
       echo "Programming error"
-      exit 3
+      exit 64
       ;;
   esac
 done