feat!: probes connect to the backend directly

A probe now links to the backend like an agent (probe.json carries the
server address). The backend sends the agent list as desired state and the
probe reports its platform and build in its own hello. The agent no longer
relays the list or the probe platform. Existing probes must be re-created.

backend/shared/Monitor.Protocol/Rpc/MonitorRpc.cs

@@ -13,8 +13,6 @@ public static class MonitorMethods
     public const string TestStatus = "monitor.test.status";
     public const string Event = "monitor.event";
     public const string Host = "monitor.host";
-    public const string ProbeAgents = "monitor.probe.agents";
-    public const string ProbeAgentsChanged = "monitor.probe.agents_changed";
 
     // Probe ↔ Agent（点对点会话）
     public const string Clock = "monitor.clock";
@@ -147,19 +145,11 @@ public sealed class AgentEndpoint
     public string Spki { get; set; } = "";
 }
 
-public sealed class ProbeAgentsParams
+/// <summary>期望状态文档（Fleet state type = <c>probe_agents</c>）：Backend 直接下发给每个 Probe 的 Agent 列表。</summary>
+public sealed class ProbeAgentList
 {
-    /// <summary>Probe 目前持有的列表版本（用于调试；服务端总是返回当前列表）。</summary>
-    [JsonPropertyName("have_version")]
-    public long HaveVersion { get; set; }
+    public const string StateType = "probe_agents";
 
-    /// <summary>Probe 的系统和架构（只用于展示；Agent 记在会话上，随连接状态报给 Backend）。</summary>
-    [JsonPropertyName("platform")]
-    public PlatformInfo? Platform { get; set; }
-}
-
-public sealed class ProbeAgentsResult
-{
     [JsonPropertyName("version")]
     public long Version { get; set; }
 
@@ -227,6 +217,13 @@ public sealed class PlatformInfo
     public string? BuiltAt { get; set; }
 }
 
+/// <summary>Probe 的 <c>fleet.hello</c> 附加字段：系统、架构和构建信息（只用于展示和更新）。</summary>
+public sealed class ProbeHelloMeta
+{
+    [JsonPropertyName("platform")]
+    public PlatformInfo? Platform { get; set; }
+}
+
 /// <summary><c>fleet.hello</c> 的附加字段。</summary>
 public sealed class AgentHelloMeta
 {
@@ -302,9 +299,6 @@ public sealed class ConnectedProbe
 
     [JsonPropertyName("since_utc_ms")]
     public long SinceUtcMs { get; set; }
-
-    [JsonPropertyName("platform")]
-    public PlatformInfo? Platform { get; set; }
 }
 
 /// <summary><c>fleet.heartbeat</c> 的附加字段：只有进程内的计数，没有主机信息。</summary>
@@ -470,8 +464,8 @@ public static class FragmentKeys
 [JsonSerializable(typeof(HostSnapshot))]
 [JsonSerializable(typeof(TestStatusParams))]
 [JsonSerializable(typeof(AgentEventParams))]
-[JsonSerializable(typeof(ProbeAgentsParams))]
-[JsonSerializable(typeof(ProbeAgentsResult))]
+[JsonSerializable(typeof(ProbeAgentList))]
+[JsonSerializable(typeof(ProbeHelloMeta))]
 [JsonSerializable(typeof(AgentEnrollMeta))]
 [JsonSerializable(typeof(PlatformInfo))]
 [JsonSerializable(typeof(AgentHelloMeta))]

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