wire: echo UDID in DataHeaders on every response

SignUpTask.Parse validates data_headers.udid against Certification.Udid;
mismatch discards the response. Sourced from the same mappedUdid the
translation middleware uses to decrypt — never controller state. Other
endpoints carry the extra key; SignUpTask is the only reader.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Models/Dtos/Internal/DataHeaders.cs

@@ -21,4 +21,15 @@ public class DataHeaders
     [JsonPropertyName("result_code")]
     [Key("result_code")]
     public int ResultCode { get; set; }
-}
+
+    /// <summary>
+    /// Echoed UDID. Read by <c>SignUpTask.Parse</c> to validate response identity (client logs
+    /// <c>udid一致しません</c> and discards the response on mismatch); ignored by every other
+    /// client task. Always set by <c>ShadowverseTranslationMiddleware</c> from the request's
+    /// resolved UDID — never from controller state. Empty string when the SID→UDID lookup misses
+    /// (request without UDID/SID headers).
+    /// </summary>
+    [JsonPropertyName("udid")]
+    [Key("udid")]
+    public string Udid { get; set; } = "";
+}