fix(chat): 채팅방 메시지 전송 API 반환값 수정

- 기존: SendChatMessageResponse으로 메시지 리스트를 한 번 더 Wrapping해서 보냄

- 수정: 메시지 리스트 반환

src/main/kotlin/kr/co/vividnext/sodalive/chat/room/dto/ChatRoomDto.kt

@@ -126,13 +126,6 @@ data class SendChatMessageRequest(
     val message: String
 )
 
-/**
- * 채팅 메시지 전송 응답 DTO (캐릭터 메시지 리스트)
- */
-data class SendChatMessageResponse(
-    val characterMessages: List<ChatMessageItemDto>
-)
-
 /**
  * 외부 API 채팅 전송 응답 DTO
  */

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

@@ -16,7 +16,6 @@ import kr.co.vividnext.sodalive.chat.room.dto.CreateChatRoomResponse
 import kr.co.vividnext.sodalive.chat.room.dto.ExternalChatSendResponse
 import kr.co.vividnext.sodalive.chat.room.dto.ExternalChatSessionCreateResponse
 import kr.co.vividnext.sodalive.chat.room.dto.ExternalChatSessionGetResponse
-import kr.co.vividnext.sodalive.chat.room.dto.SendChatMessageResponse
 import kr.co.vividnext.sodalive.chat.room.repository.ChatMessageRepository
 import kr.co.vividnext.sodalive.chat.room.repository.ChatParticipantRepository
 import kr.co.vividnext.sodalive.chat.room.repository.ChatRoomRepository
@@ -476,7 +475,7 @@ class ChatRoomService(
     }
 
     @Transactional
-    fun sendMessage(member: Member, chatRoomId: Long, message: String): SendChatMessageResponse {
+    fun sendMessage(member: Member, chatRoomId: Long, message: String): List<ChatMessageItemDto> {
         // 1) 방 존재 확인
         val room = chatRoomRepository.findById(chatRoomId).orElseThrow {
             SodaException("채팅방을 찾을 수 없습니다.")
@@ -533,7 +532,7 @@ class ChatRoomService(
                 ?: 0L
         )
 
-        return SendChatMessageResponse(characterMessages = listOf(dto))
+        return listOf(dto)
     }
 
     private fun callExternalApiForChatSendWithRetry(