사용자 관리 포트 제거 및 발신자 이름 로직 최적화

- `LetterQueryService`와 `LetterCommandService`에서 `UserManagementPort` 삭제.
- `senderName` 기본값 처리 로직 단순화 (`ANONYMOUS_SENDER_NAME` 사용).
- 엔터티(`ReceiveLetterEntity`, `SendLetterEntity`)에서 `senderName`을 `sender?.username` 기반으로 계산하도록 수정.
- 불필요한 변수와 로직 제거로 코드 최적화.

Author: tlarbals824

Application-Module/src/main/kotlin/com/asap/application/letter/service/LetterCommandService.kt

@@ -106,16 +106,13 @@ class LetterCommandService(
                 receiverId = DomainId(command.userId),
                 letterId = DomainId(command.letterId),
             )
+
         val independentLetter =
             IndependentLetter.create(
                 sender =
                     SenderInfo(
                         senderId = sendLetter.senderId,
-                        senderName =
-                            sendLetter.senderName
-                                ?: sendLetter.senderId
-                                    ?.let { userManagementPort.getUserNotNull(it).username }
-                                    .orEmpty(),
+                        senderName = sendLetter.senderName ?: ANONYMOUS_SENDER_NAME,
                     ),
                 receiver =
                     ReceiverInfo(

Application-Module/src/main/kotlin/com/asap/application/letter/service/LetterQueryService.kt

@@ -5,7 +5,6 @@ import com.asap.application.letter.port.out.IndependentLetterManagementPort
 import com.asap.application.letter.port.out.SendLetterManagementPort
 import com.asap.application.letter.port.out.SpaceLetterManagementPort
 import com.asap.application.space.port.out.SpaceManagementPort
-import com.asap.application.user.port.out.UserManagementPort
 import com.asap.common.page.PageRequest
 import com.asap.common.page.Sort
 import com.asap.domain.common.DomainId
@@ -16,7 +15,6 @@ import org.springframework.transaction.annotation.Transactional
 @Transactional(readOnly = true)
 class LetterQueryService(
     private val sendLetterManagementPort: SendLetterManagementPort,
-    private val userManagementPort: UserManagementPort,
     private val independentLetterManagementPort: IndependentLetterManagementPort,
     private val spaceLetterManagementPort: SpaceLetterManagementPort,
     private val spaceManagementPort: SpaceManagementPort,
@@ -32,9 +30,8 @@ class LetterQueryService(
                 receiverId = DomainId(query.userId),
                 letterId = DomainId(query.letterId),
             ).also {
-                val sender = it.senderId?.let { userManagementPort.getUserNotNull(it) }
                 return GetVerifiedLetterUsecase.Response(
-                    senderName = sender?.username,
+                    senderName = it.senderName,
                     content = it.content.content,
                     sendDate = it.createdDate,
                     templateType = it.content.templateType,
@@ -76,7 +73,7 @@ class LetterQueryService(
             independentLetterManagementPort.getNearbyLetter(DomainId(query.userId), DomainId(query.letterId))
         return GetIndependentLettersUsecase.Response.One(
             senderName = letter.sender.senderName,
-            letterCount = letterCount.toLong(),
+            letterCount = letterCount,
             content = letter.content.content,
             sendDate = letter.receiveDate,
             images = letter.content.images,

Infrastructure-Module/Persistence/src/main/kotlin/com/asap/persistence/jpa/letter/entity/ReceiveLetterEntity.kt

@@ -53,7 +53,9 @@ class ReceiveLetterEntity(
     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "sender_id", insertable = false, updatable = false)
     var sender: UserEntity? = null
+
     var senderName: String = senderName
+        get() = sender?.username ?: field
 
     @Column(
         name = "receiver_id",

Infrastructure-Module/Persistence/src/main/kotlin/com/asap/persistence/jpa/letter/entity/SendLetterEntity.kt

@@ -55,6 +55,7 @@ class SendLetterEntity(
 
     @Column(name = "sender_name")
     var senderName: String? = senderName
+        get() = sender?.username ?: field
 
     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(