build: .dockerignore, pin guarddog>=2.10.0, Docker HEALTHCHECK

Dockerfile

@@ -11,7 +11,7 @@ COPY pyproject.toml README.md ./
 COPY guarddog_nexus/ guarddog_nexus/
 
 RUN uv pip install . --system
-RUN uv pip install --system guarddog
+RUN uv pip install --system "guarddog>=2.10.0"
 
 RUN mkdir -p /data /tmp/guarddog-nexus
 
@@ -21,4 +21,7 @@ ENV PYTHONDONTWRITEBYTECODE=1
 
 EXPOSE 8080
 
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+    CMD python -c "from urllib.request import urlopen; urlopen('http://localhost:8080/health')"
+
 CMD ["python", "-m", "guarddog_nexus.main"]