Redirect HF model cache to persistent storage on /data/hf_cache

Avoids re-downloading ~20GB of model weights on every cold start.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.py

@@ -1,6 +1,8 @@
 import os
 import gc
 import threading
+
+os.environ.setdefault("HF_HOME", "/data/hf_cache")
 import gradio as gr
 import numpy as np
 import spaces