feat!: probes link to the panel; signed release updates for container nodes [CI]

Probes connect to the panel directly and get the agent list as desired state.
CI signs the image digest of agent and probe releases, the panel forwards the
manifest, and a host updater verifies it with a local public key, pulls by
digest and rolls back when the new version is unhealthy.

backend/shared/Monitor.Protocol/Tasks/TaskSet.cs

@@ -56,9 +56,6 @@ public sealed class TaskSet
     /// <summary>允许连接到这个 Agent 的 Probe 公钥。</summary>
     [JsonPropertyName("peers")]
     public List<PeerSpec> Peers { get; set; } = [];
-
-    [JsonPropertyName("probe_agents_version")]
-    public long ProbeAgentsVersion { get; set; }
 }
 
 public static class TaskSchedule