Ensure data directory exists before chown

Dockerfile

@@ -141,7 +141,7 @@ RUN pip3 install --no-cache-dir uv && \
     else \
     uv pip install --system -r requirements.txt --no-cache-dir; \
     fi; \
-    chown -R $UID:$GID /app/backend/data/
+    mkdir -p /app/backend/data && chown -R $UID:$GID /app/backend/data/
 
 # Install Ollama if requested
 RUN if [ "$USE_OLLAMA" = "true" ] && [ "$USE_SLIM" != "true" ]; then \