feat(be) : WebSocket 설정 삭제 및 entity, repository 추가

src/main/kotlin/com/back/koreaTravelGuide/domain/userChat/chatmessage/entity/ChatMessage.kt

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+package com.back.koreaTravelGuide.domain.userChat.chatmessage.entity
+
+import jakarta.persistence.Column
+import jakarta.persistence.Entity
+import jakarta.persistence.GeneratedValue
+import jakarta.persistence.GenerationType
+import jakarta.persistence.Id
+import jakarta.persistence.Index
+import jakarta.persistence.Table
+import java.time.Instant
+
+@Entity
+@Table(
+    name = "userchat_message",
+    indexes = [Index(name = "ix_msg_room_id_id", columnList = "room_id,id")],
+)
+data class ChatMessage(
+    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
+    val id: Long? = null,
+    @Column(name = "room_id", nullable = false)
+    val roomId: Long,
+    @Column(name = "sender_id", nullable = false)
+    val senderId: Long,
+    @Column(columnDefinition = "text", nullable = false)
+    val content: String,
+    @Column(name = "created_at", nullable = false)
+    val createdAt: Instant = Instant.now(),
+)

src/main/kotlin/com/back/koreaTravelGuide/domain/userChat/chatmessage/repository/ChatMessageRepository.kt

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+package com.back.koreaTravelGuide.domain.userChat.chatmessage.repository
+
+import com.back.koreaTravelGuide.domain.userChat.chatmessage.entity.ChatMessage
+import org.springframework.data.jpa.repository.JpaRepository
+
+interface ChatMessageRepository : JpaRepository<ChatMessage, Long> {
+    fun findTop50ByRoomIdOrderByIdDesc(roomId: Long): List<ChatMessage>
+
+    fun findByRoomIdAndIdGreaterThanOrderByIdAsc(
+        roomId: Long,
+        afterId: Long,
+    ): List<ChatMessage>
+}

src/main/kotlin/com/back/koreaTravelGuide/domain/userChat/chatroom/entity/ChatRoom.kt

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+package com.back.koreaTravelGuide.domain.userChat.chatroom.entity
+
+import jakarta.persistence.Column
+import jakarta.persistence.Entity
+import jakarta.persistence.GeneratedValue
+import jakarta.persistence.GenerationType
+import jakarta.persistence.Id
+import jakarta.persistence.Index
+import jakarta.persistence.Table
+import java.time.Instant
+
+@Entity
+@Table(
+    name = "userchat_room",
+    indexes = [Index(name = "ix_room_updated_at", columnList = "updated_at")],
+)
+data class ChatRoom(
+    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
+    val id: Long? = null,
+    @Column(nullable = false)
+    val title: String,
+    @Column(name = "owner_id", nullable = false)
+    val ownerId: Long,
+    @Column(name = "updated_at", nullable = false)
+    val updatedAt: Instant = Instant.now(),
+    @Column(name = "last_message_id")
+    val lastMessageId: Long? = null,
+)

src/main/kotlin/com/back/koreaTravelGuide/domain/userChat/chatroom/repository/ChatRoomRepository.kt

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+package com.back.koreaTravelGuide.domain.userChat.chatroom.repository
+
+import com.back.koreaTravelGuide.domain.userChat.chatroom.entity.ChatRoom
+import org.springframework.data.jpa.repository.JpaRepository
+
+interface ChatRoomRepository : JpaRepository<ChatRoom, Long>