Fix: Set writable cache directory for HuggingFace downloads

Fixes permission denied errors when downloading dataset files.
Sets HF_HOME and related cache paths to /tmp which is writable in Docker.

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

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

Dockerfile

@@ -2,6 +2,11 @@ FROM python:3.10-slim
 
 WORKDIR /app
 
+# Set Hugging Face cache to writable directory
+ENV HF_HOME=/tmp/huggingface
+ENV TRANSFORMERS_CACHE=/tmp/huggingface/transformers
+ENV HF_DATASETS_CACHE=/tmp/huggingface/datasets
+
 # Install system dependencies
 RUN apt-get update && apt-get install -y \
     git \