feat: node info, build info and acrylic web theme

Squash of recent dev work: return_session login, backend switcher, line
detail timeline, overview strips, node platform/country/ISP info with flags
and icons, build info (version, tag, time) behind site.show_build, and the
acrylic display theme.

backend/shared/Monitor.Protocol/Monitor.Protocol.csproj

@@ -6,4 +6,30 @@
     <ProjectReference Include="..\..\fleet\src\Fleet.Core\Fleet.Core.csproj" />
     <ProjectReference Include="..\..\fleet\src\Fleet.Rpc\Fleet.Rpc.csproj" />
   </ItemGroup>
+  <!--
+    构建信息：版本来自 $(Version)，tag、提交、构建时间来自环境变量 MONITOR_TAG / MONITOR_COMMIT / MONITOR_BUILT_AT
+    （scripts/publish.sh 和 CI 会设置；本地开发不设置就是空，这样本地构建是可重复的、不会每次都重新编译）。
+    生成一个带常量的源文件，NativeAOT 下不用反射。
+  -->
+  <Target Name="WriteBuildInfo" BeforeTargets="CoreCompile">
+    <PropertyGroup>
+      <BuildInfoFile>$(IntermediateOutputPath)BuildInfo.g.cs</BuildInfoFile>
+    </PropertyGroup>
+    <ItemGroup>
+      <BuildInfoLine Include="namespace Monitor.Protocol%3B" />
+      <BuildInfoLine Include="/// &lt;summary&gt;这个程序是什么时候、从哪个版本构建出来的（构建时生成）。&lt;/summary&gt;" />
+      <BuildInfoLine Include="public static class BuildInfo" />
+      <BuildInfoLine Include="{" />
+      <BuildInfoLine Include="    public const string Version = &quot;$(Version)&quot;%3B" />
+      <BuildInfoLine Include="    public const string Tag = &quot;$(MONITOR_TAG)&quot;%3B" />
+      <BuildInfoLine Include="    public const string Commit = &quot;$(MONITOR_COMMIT)&quot;%3B" />
+      <BuildInfoLine Include="    public const string BuiltAt = &quot;$(MONITOR_BUILT_AT)&quot;%3B" />
+      <BuildInfoLine Include="}" />
+    </ItemGroup>
+    <WriteLinesToFile File="$(BuildInfoFile)" Lines="@(BuildInfoLine)" Overwrite="true" WriteOnlyWhenDifferent="true" />
+    <ItemGroup>
+      <Compile Include="$(BuildInfoFile)" />
+      <FileWrites Include="$(BuildInfoFile)" />
+    </ItemGroup>
+  </Target>
 </Project>