Simplify build script directory validation

- Replace file-based validation with directory name check
- Now simply checks if current directory is named 'nostr_core_lib'
- More reliable and clearer error messages for customers
- Fixes issue where customers get validation errors when running from properly named directories

build.sh

@@ -148,10 +148,13 @@ fi
 print_info "NOSTR Core Library - Customer Build Script"
 
 # Check if we're running from the correct directory
-if [ ! -d "nostr_core" ] || [ ! -f "nostr_core/utils.c" ] || [ ! -d "secp256k1" ]; then
+CURRENT_DIR=$(basename "$(pwd)")
+if [ "$CURRENT_DIR" != "nostr_core_lib" ]; then
     print_error "Build script must be run from the nostr_core_lib directory"
     echo ""
-    echo "It looks like you're trying to run this script from your project directory."
+    echo "Current directory: $CURRENT_DIR"
+    echo "Expected directory: nostr_core_lib"
+    echo ""
     echo "Please change to the nostr_core_lib directory first, then run the build script."
     echo ""
     echo "Correct usage:"