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/probe/src/Monitor.Probe/Link/AgentConnection.cs

@@ -163,10 +163,13 @@ public sealed class AgentConnection
         }
     }
 
+    /// <summary>本机的系统和架构：随列表同步一起告诉 Agent，只用于在面板上展示。</summary>
+    private static readonly PlatformInfo s_platform = PlatformDetector.Detect();
+
     private async Task RefreshDirectoryAsync(RpcSession<ConnectionSession> rpc, CancellationToken ct)
     {
         Result<ProbeAgentsResult> list = await rpc.RequestAsync(
-            MonitorMethods.ProbeAgents, new ProbeAgentsParams { HaveVersion = _env.Directory.Version }, MonitorJsonContext.Default.ProbeAgentsParams, MonitorJsonContext.Default.ProbeAgentsResult, ct);
+            MonitorMethods.ProbeAgents, new ProbeAgentsParams { HaveVersion = _env.Directory.Version, Platform = s_platform }, MonitorJsonContext.Default.ProbeAgentsParams, MonitorJsonContext.Default.ProbeAgentsResult, ct);
         if (list.TryGet(out ProbeAgentsResult? agents, out FleetError? error))
         {
             _env.Directory.Apply(agents);

backend/probe/src/Monitor.Probe/ProbeApp.cs

@@ -11,7 +11,7 @@ namespace Monitor.Probe;
 /// </summary>
 public sealed class ProbeApp : IDisposable
 {
-    public const string Version = "0.1.1";
+    public const string Version = Monitor.Protocol.BuildInfo.Version;
 
     private readonly ConnectionEnv _env;
     private readonly Dictionary<string, Running> _connections = [];