fix(ingress): enable unbuffered Python output for real-time logging

Python stdout is fully buffered when not connected to a terminal (e.g.
in Docker containers). This causes log output to be delayed and appear
in batches, making it hard to diagnose timing issues.

Set PYTHONUNBUFFERED=1 so print() output appears immediately in
container logs.

Author: kvinwang

custom-domain/dstack-ingress/Dockerfile

@@ -58,6 +58,7 @@ RUN --mount=type=bind,source=scripts,target=/tmp/scripts,ro \
 
 ENV PATH="/scripts:$PATH"
 ENV PYTHONPATH="/scripts"
+ENV PYTHONUNBUFFERED=1
 COPY --chmod=666 .GIT_REV /etc/
 
 ENTRYPOINT ["/scripts/entrypoint.sh"]