fix: create and grant permissions for /app/output to avoid PermissionError

* Added mkdir and chmod for /app/output alongside /app/backend/output
* Ensures Hugging Face Spaces runtime user can write to output folder
* Prevents PermissionError: [Errno 13] Permission denied: '/app/output'

Dockerfile

@@ -13,7 +13,8 @@ ENV PYTHONUNBUFFERED=1 \
     PYTHONDONTWRITEBYTECODE=1 \
     PIP_NO_CACHE_DIR=1
 
-RUN mkdir -p /app/backend/output && chmod -R 777 /app/backend/output
+RUN mkdir -p /app/output /app/backend/output && chmod -R 777 /app/output /app/backend/output
+