Add trust_remote_code=True for Vectara hallucination model

Vectara model uses custom code — required flag for both the Dockerfile
pre-download step and the CrossEncoder constructor in grader.py.

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

Dockerfile

@@ -12,7 +12,7 @@ RUN pip install --no-cache-dir -r requirements.txt
 
 # Pre-download models so first request isn't slow on HF Spaces
 RUN python -c "from sentence_transformers import SentenceTransformer; SentenceTransformer('all-MiniLM-L6-v2')"
-RUN python -c "from sentence_transformers import CrossEncoder; CrossEncoder('vectara/hallucination_evaluation_model')"
+RUN python -c "from sentence_transformers import CrossEncoder; CrossEncoder('vectara/hallucination_evaluation_model', trust_remote_code=True)"
 
 COPY knowledge/ ./knowledge/
 COPY backend/   ./backend/

backend/grader.py

@@ -39,7 +39,7 @@ def get_nli_model() -> CrossEncoder:
     """Return the shared NLI cross-encoder, loading it on first call."""
     global _nli_model
     if _nli_model is None:
-        _nli_model = CrossEncoder(NLI_MODEL)
+        _nli_model = CrossEncoder(NLI_MODEL, trust_remote_code=True)
     return _nli_model