fix(chat): 외부 채팅 API 요청에 username을 전달한다

src/main/kotlin/kr/co/vividnext/sodalive/chat/room/service/ChatRoomService.kt

@@ -672,7 +672,7 @@ class ChatRoomService(
         )
 
         // 6) 외부 API 호출 (최대 3회 재시도)
-        val characterReply = callExternalApiForChatSendWithRetry(userId, characterUUID, message, sessionId)
+        val characterReply = callExternalApiForChatSendWithRetry(userId, member.nickname, characterUUID, message, sessionId)
 
         // 6) 내 메시지 저장
         val myMsgEntity = ChatMessage(
@@ -827,6 +827,7 @@ class ChatRoomService(
 
     private fun callExternalApiForChatSendWithRetry(
         userId: String,
+        username: String,
         characterUUID: String,
         message: String,
         sessionId: String
@@ -836,7 +837,7 @@ class ChatRoomService(
         while (attempt < maxAttempts) {
             attempt++
             try {
-                return callExternalApiForChatSend(userId, characterUUID, message, sessionId)
+                return callExternalApiForChatSend(userId, username, characterUUID, message, sessionId)
             } catch (e: Exception) {
                 log.warn("[chat] 외부 채팅 전송 실패 attempt={}, error={}", attempt, e.message)
             }
@@ -847,6 +848,7 @@ class ChatRoomService(
 
     private fun callExternalApiForChatSend(
         userId: String,
+        username: String,
         characterUUID: String,
         message: String,
         sessionId: String
@@ -863,6 +865,7 @@ class ChatRoomService(
 
         val requestBody = mapOf(
             "userId" to userId,
+            "username" to username,
             "characterId" to characterUUID,
             "message" to message,
             "sessionId" to sessionId