Add HF_TOKEN auth for private model repo access

Login to HuggingFace Hub using HF_TOKEN env var (set as Space secret).

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

backend/appfunc.py

@@ -4,7 +4,11 @@ import traceback
 import gradio as gr
 import os.path as osp
 
-from huggingface_hub import hf_hub_download, list_repo_files
+from huggingface_hub import hf_hub_download, list_repo_files, login
+
+HF_TOKEN = os.environ.get("HF_TOKEN", None)
+if HF_TOKEN:
+    login(token=HF_TOKEN)
 
 from omegaconf import OmegaConf
 from refnet.util import instantiate_from_config