feat: add cross-platform release pipeline [CI SKIP]

packaging/container/Backend.Containerfile

@@ -0,0 +1,20 @@
+FROM mcr.microsoft.com/dotnet/aspnet:10.0-noble-chiseled-extra
+
+ARG APP_VERSION=unknown
+LABEL org.opencontainers.image.title="Monitor Backend" \
+      org.opencontainers.image.description="Self-hosted network path quality monitoring backend" \
+      org.opencontainers.image.licenses="Apache-2.0" \
+      org.opencontainers.image.version="$APP_VERSION"
+
+WORKDIR /app
+COPY --chown=1654:1654 app/ /app/
+COPY --chown=1654:1654 data/.keep /data/.keep
+
+ENV ASPNETCORE_HTTP_PORTS=8080 \
+    Monitor__DataDirectory=/data \
+    DOTNET_EnableDiagnostics=0
+
+USER 1654:1654
+VOLUME ["/data"]
+EXPOSE 8080
+ENTRYPOINT ["dotnet", "/app/monitor-backend.dll"]