chore(docker): add HEALTHCHECK probe to UI image

Python urllib GET / on 127.0.0.1:8080. start_period=30s
gives uvicorn time to boot. Lets Docker mark container
unhealthy if webui wedges, and feeds Portainer +
diagnose.sh signal that the app is alive.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Dockerfile

@@ -35,5 +35,8 @@ RUN git init /vault && \
 
 EXPOSE 8080
 
+HEALTHCHECK --interval=30s --timeout=5s --retries=3 --start-period=30s \
+    CMD python -c "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8080/').close()" || exit 1
+
 ENTRYPOINT ["/work/entrypoint.sh"]
 CMD ["uvicorn", "webui:app", "--host", "0.0.0.0", "--port", "8080"]