Add Docker startup diagnostics

Dockerfile

@@ -18,6 +18,7 @@ RUN pip install --no-cache-dir --upgrade pip \
     && pip install --no-cache-dir -r requirements.txt
 
 COPY app.py .
+RUN python -m py_compile app.py
 
 EXPOSE 7860
-CMD ["python", "app.py"]
+CMD ["/bin/sh", "-c", "echo codex-traces docker cmd start >&2; python -u app.py"]