fix(build): set NLTK_DATA to writable path and pre-download punkt

Dockerfile

@@ -15,8 +15,10 @@ ARG HF_MODEL_REPO=Jaja-09/authorcheck-model
 # Download model snapshot from HF model repo
 RUN python -c "from huggingface_hub import snapshot_download; snapshot_download(repo_id='${HF_MODEL_REPO}', local_dir='/app/model')"
 
-# Ensure NLTK tokenizer data is present
-RUN python -c "import nltk; nltk.download('punkt', quiet=True)"
+# Pre-download NLTK data to a writable path and set env
+ENV NLTK_DATA=/app/nltk_data
+RUN mkdir -p /app/nltk_data && \
+    python -c "import nltk; nltk.download('punkt', download_dir='/app/nltk_data', quiet=True)"
 
 EXPOSE 7860
 CMD ["uvicorn", "app:app", "--host", "0.0.0.0", "--port", "7860"]