Fix /data directory permissions for HF Spaces

- Create /data directory with write permissions
- Fixes sqlite3.OperationalError: unable to open database file

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Dockerfile

@@ -9,5 +9,8 @@ ENV MODEL_FILENAME=phi4-mini-instruct-Q4_K_M.gguf
 ENV USE_RAG=true
 ENV CACHE_ENABLED=true
 
+# Ensure /data directory exists and is writable
+RUN mkdir -p /data && chmod 777 /data
+
 EXPOSE 8000
 CMD ["python", "main.py"]