fix(link): ride out short path blackouts: 30s handshake, 180s idle limit, 90s keepalive, faster probe reconnect [CI]

backend/probe/src/MoShiro.Probe/Link/AgentConnection.cs

@@ -47,7 +47,8 @@ public sealed class AgentConnection
 
     public async Task RunAsync(CancellationToken ct)
     {
-        var backoff = new Backoff(TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(20));
+        // 重连的间隔别拉太长：每次尝试本来就要等好几秒（握手上限 30 秒），线路一恢复要尽快接上；带抖动，不会和别的节点撞在一起
+        var backoff = new Backoff(TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(8));
         while (!ct.IsCancellationRequested)
         {
             try