Fix: pin transformers==4.40.2 for PyTorch 2.1 compatibility

auto_train.sh

@@ -64,8 +64,8 @@ if [[ "$PYTORCH_VERSION" == "none" ]]; then
 else
   echo "  Using existing PyTorch $PYTORCH_VERSION (skipping reinstall)"
 fi
-# Install other deps without touching torch
-pip install -q transformers pillow pandas requests tqdm scikit-learn huggingface_hub datasets 2>&1 | tail -3
+# Install other deps - pin transformers to version compatible with PyTorch 2.1
+pip install -q "transformers==4.40.2" pillow pandas requests tqdm scikit-learn huggingface_hub datasets 2>&1 | tail -3
 echo "  ✓ Dependencies installed"
 
 # ── Step 2: Download CIFAKE dataset ──────────────────────────