feat(chat-room-list): 이미지 메시지면 최근 메시지를 [이미지]로 표시

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

@@ -251,9 +251,17 @@ class ChatRoomService(
             ).apply { id = q.chatRoomId }
 
             val latest = messageRepository.findTopByChatRoomAndIsActiveTrueOrderByCreatedAtDesc(room)
-            val preview = latest?.message?.let { msg ->
+            val preview = if (latest?.message?.isNotBlank() == true) {
+                latest.message.let { msg ->
                     if (msg.length <= 30) msg else msg.take(30) + "..."
                 }
+            } else {
+                if (latest?.message.isNullOrBlank() && latest?.characterImage != null) {
+                    "[이미지]"
+                } else {
+                    ""
+                }
+            }
 
             val imageUrl = "$imageHost/${q.imagePath ?: "profile/default-profile.png"}"
             val opponentType = q.characterType.name // Clone or Character