feat(backend): report node platform, geo and build info

Agents and probes report OS, arch and build (version, tag, commit, time).
The backend looks up country and ISP of public addresses only, stores them
in node_meta (schema v5) and exposes display info via /api/public/nodes,
/api/public/about and /api/admin/build-info behind site.show_build.

packaging/container/Probe.Fastlane.Containerfile

@@ -1,6 +1,11 @@
 FROM mcr.microsoft.com/dotnet/sdk:10.0-noble-aot AS build
 
 WORKDIR /src/backend
+# 构建信息：CI 通过 --build-arg 传入；不传就是空
+ARG MONITOR_TAG=
+ARG MONITOR_COMMIT=
+ARG MONITOR_BUILT_AT=
+ENV MONITOR_TAG=$MONITOR_TAG MONITOR_COMMIT=$MONITOR_COMMIT MONITOR_BUILT_AT=$MONITOR_BUILT_AT
 COPY restore/backend/ ./
 RUN dotnet restore probe/src/Monitor.Probe -r linux-x64 --artifacts-path /artifacts