build.sh: fix empty array expansion under set -u

${arr[@]} with set -u throws 'unbound variable' when the array is empty.
Use ${arr[@]+"${arr[@]}"} which only expands if the array is set.

https://claude.ai/code/session_01FKCW3FDjNFj6jve4niMFXH

builder/build.sh

@@ -99,7 +99,7 @@ fi
 docker run --detach \
     --name "$CONTAINER_NAME" \
     --network hiy-net \
-    "${ENV_FILE_ARG[@]}" \
+    "${ENV_FILE_ARG[@]+"${ENV_FILE_ARG[@]}"}" \
     --expose "$PORT" \
     --label "hiy.app=${APP_ID}" \
     --label "hiy.port=${PORT}" \