fix: Pin huggingface_hub to compatible version for Gradio OAuth

- Pin huggingface_hub>=0.25,<1.0 in requirements.txt and pyproject.toml
- Ensures HfFolder import is available for Gradio OAuth

pyproject.toml

@@ -61,6 +61,7 @@ api = [
 ]
 ui = [
     "gradio>=4.0.0",
+    "huggingface_hub>=0.25,<1.0",
 ]
 all = [
     "ptpd-calibration[ml,llm,api,ui]",

requirements.txt

@@ -7,6 +7,7 @@ pydantic-settings>=2.1.0
 
 # UI
 gradio>=4.0.0
+huggingface_hub>=0.25,<1.0
 
 # ML (optional but useful)
 scikit-learn>=1.3.0