fix: PYTHONUNBUFFERED=1 so progress bars stream in real-time

Python buffers stdout by default. Docker only sees the buffer dumps,
so all progress bars appear at once when the step completes.
PYTHONUNBUFFERED=1 disables buffering — prints flush immediately.

docker-compose.yml

@@ -8,7 +8,7 @@ services:
     environment:
       - OMP_NUM_THREADS=128
       - CUDA_LAUNCH_BLOCKING=0
-      - TORCH_SHOW_CPP_STACKTRACES=0
+      - PYTHONUNBUFFERED=1
     command:
       - /model
       - --trust-remote-code