Add knowledge_db directory and remove deprecated env var

- Create /app/knowledge_db directory with write permissions
- Remove deprecated TRANSFORMERS_CACHE env var (use HF_HOME instead)
- Fixes PermissionError: [Errno 13] Permission denied: './knowledge_db'

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

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

Dockerfile

@@ -11,12 +11,10 @@ ENV CACHE_ENABLED=true
 
 # Set Hugging Face cache to /data for persistence and write permissions
 ENV HF_HOME=/data/huggingface
-ENV TRANSFORMERS_CACHE=/data/huggingface/transformers
-ENV HF_HUB_CACHE=/data/huggingface/hub
 
 # Ensure all required directories exist and are writable
-RUN mkdir -p /data /app/models /data/huggingface/hub /data/huggingface/transformers && \
-    chmod -R 777 /data /app/models
+RUN mkdir -p /data /app/models /app/knowledge_db /data/huggingface/hub /data/huggingface/transformers && \
+    chmod -R 777 /data /app/models /app/knowledge_db
 
 EXPOSE 8000
 CMD ["python", "main.py"]