feat(chat): DM 채팅 메시지 매퍼를 추가한다

app/src/main/java/kr/co/vividnext/sodalive/v2/main/chat/dm/model/DmChatMappers.kt

@@ -0,0 +1,38 @@
+package kr.co.vividnext.sodalive.v2.main.chat.dm.model
+
+import kr.co.vividnext.sodalive.v2.main.chat.dm.data.DmChatMessageResponse
+
+private const val MESSAGE_TYPE_TEXT = "TEXT"
+
+fun DmChatMessageResponse.toUiItem(): DmChatMessageUiItem? {
+    if (!messageType.equals(MESSAGE_TYPE_TEXT, ignoreCase = true) || textMessage == null) return null
+
+    return DmChatMessageUiItem(
+        messageId = messageId,
+        localId = null,
+        mine = mine,
+        textMessage = textMessage,
+        senderNickname = senderNickname,
+        senderProfileImageUrl = senderProfileImageUrl,
+        createdAt = createdAt,
+        status = DmChatMessageStatus.SENT
+    )
+}
+
+fun List<DmChatMessageResponse>.toUiItems(): List<DmChatMessageUiItem> = mapNotNull { it.toUiItem() }
+
+/** Sorts messages by server creation time, then by messageId for same-time messages. */
+fun List<DmChatMessageUiItem>.sortByCreatedAtAndMessageId(): List<DmChatMessageUiItem> =
+    sortedWith(compareBy<DmChatMessageUiItem> { it.createdAt }.thenBy { it.messageId ?: Long.MAX_VALUE })
+
+/** Merges new messages while keeping the first-arrived item when server messageId duplicates. */
+fun List<DmChatMessageUiItem>.mergeByMessageId(
+    incoming: List<DmChatMessageUiItem>
+): List<DmChatMessageUiItem> {
+    val seenMessageIds = mapNotNull { it.messageId }.toMutableSet()
+    val newItems = incoming.filter { item ->
+        val messageId = item.messageId
+        messageId == null || seenMessageIds.add(messageId)
+    }
+    return (this + newItems).sortByCreatedAtAndMessageId()
+}

app/src/main/java/kr/co/vividnext/sodalive/v2/main/chat/dm/model/DmChatUiModels.kt

@@ -0,0 +1,18 @@
+package kr.co.vividnext.sodalive.v2.main.chat.dm.model
+
+enum class DmChatMessageStatus {
+    SENDING,
+    SENT,
+    FAILED
+}
+
+data class DmChatMessageUiItem(
+    val messageId: Long?,
+    val localId: String?,
+    val mine: Boolean,
+    val textMessage: String,
+    val senderNickname: String,
+    val senderProfileImageUrl: String,
+    val createdAt: Long,
+    val status: DmChatMessageStatus
+)