Restore huggingface_hub<1.0 pin (gradio 5.0.x still uses HfFolder)

requirements.txt

@@ -6,4 +6,6 @@ torchinfo>=1.8
 gradio>=5.0
 docutils>=0.20
 mne>=1.11
-huggingface_hub>=0.23
+# Gradio 5.0.x still imports HfFolder (removed only in huggingface_hub 1.0+).
+# Pin until we move to a gradio version that drops the legacy import.
+huggingface_hub>=0.23,<1.0