feat!: pre-handshake knock on the agent TCP ports; probes get the agent certificate public key [CI]

backend/probe/src/MoShiro.Probe/ProbeConfig.cs

@@ -48,9 +48,9 @@ public sealed class KnownAgent
     [JsonPropertyName("tcp_port")]
     public int TcpPort { get; set; }
 
-    /// <summary>Agent 的 TLS 证书指纹（SHA-256，base64）。</summary>
-    [JsonPropertyName("spki")]
-    public string Spki { get; set; } = "";
+    /// <summary>Agent 的 TLS 证书公钥（SPKI，base64）：证书按它的 SHA-256 指纹固定，敲门密钥由它派生。</summary>
+    [JsonPropertyName("public_key")]
+    public string PublicKey { get; set; } = "";
 }
 
 public sealed class ProbeLimits