Add Dockerfile building nginx from source on port 7860

Dockerfile

@@ -0,0 +1,26 @@
+FROM ubuntu:22.04
+
+ENV DEBIAN_FRONTEND=noninteractive \
+    LISTEN_PORT=7860 \
+    UPSTREAM_URL=http://127.0.0.1:5000/
+
+# Build toolchain + gettext-base (envsubst) + python3 for the demo upstream.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+      build-essential libpcre3 libpcre3-dev zlib1g zlib1g-dev \
+      libssl-dev wget curl ca-certificates gettext-base python3 procps \
+    && rm -rf /var/lib/apt/lists/*
+
+# Build nginx from source using the spec'd installer. In a container there is
+# no systemd, so the unit file is written but never started; the entrypoint
+# runs nginx in the foreground instead. LISTEN_PORT=7860 matches app_port.
+COPY install-nginx.sh /opt/install-nginx.sh
+RUN chmod +x /opt/install-nginx.sh \
+    && LISTEN_PORT=7860 UPSTREAM_URL=http://127.0.0.1:5000/ /opt/install-nginx.sh
+
+COPY demo_upstream.py /opt/demo_upstream.py
+COPY docker-entrypoint.sh /opt/docker-entrypoint.sh
+RUN chmod +x /opt/docker-entrypoint.sh
+
+EXPOSE 7860
+
+CMD ["/opt/docker-entrypoint.sh"]