Fix Dockerfile: use preload script instead of inline python -c to avoid IndentationError

Dockerfile

@@ -30,11 +30,8 @@ COPY . .
 
 # Run a python script to pre-download the ML models to the cache folder during Docker build
 # This makes container startup immediate and avoids download timeouts.
-RUN python -c " \
-from sentence_transformers import SentenceTransformer; \
-SentenceTransformer('NeuML/pubmedbert-base-embeddings'); \
-SentenceTransformer('cross-encoder/ms-marco-MiniLM-L-6-v2'); \
-"
+COPY scripts/preload_models.py /tmp/preload_models.py
+RUN python /tmp/preload_models.py
 
 # Set permissions for the app folder again
 RUN chmod -R 777 /app