fix: pin transformers<5 for google/umt5-base compat (no model_type in config)

Dockerfile

@@ -7,7 +7,7 @@ RUN apt-get update && apt-get install -y \
 RUN pip3 install --no-cache-dir \
     torch torchvision torchaudio --index-url https://download.pytorch.org/whl/cu121 && \
     pip3 install --no-cache-dir \
-    flask flask-cors numpy transformers accelerate sentencepiece protobuf \
+    flask flask-cors numpy "transformers>=4.40,<5" accelerate sentencepiece protobuf \
     lightning omegaconf safetensors diffusers ftfy regex
 
 # Create non-root user (HF Spaces runs as uid 1000)