feat: 테마 서비스 내 조회 기능 추가

src/main/kotlin/roomescape/theme/business/ThemeServiceV2.kt

@@ -57,13 +57,21 @@ class ThemeServiceV2(
 
         val theme: ThemeEntityV2 = findOrThrow(id)
 
-        val createdBy = memberService.findById(theme.createdBy).name
-        val updatedBy = memberService.findById(theme.updatedBy).name
+        val createdBy = memberService.findSummaryById(theme.createdBy).name
+        val updatedBy = memberService.findSummaryById(theme.updatedBy).name
 
         return theme.toAdminThemeDetailResponse(createdBy, updatedBy)
             .also { log.info { "[ThemeService.findAdminThemeDetail] 테마 상세 조회 완료: id=$id, name=${theme.name}" } }
     }
 
+    @Transactional(readOnly = true)
+    fun findById(id: Long): ThemeRetrieveResponseV2 {
+        log.info { "[ThemeService.findById] 테마 조회 시작: id=$id" }
+
+        return findOrThrow(id).toRetrieveResponse()
+            .also { log.info { "[ThemeService.findById] 테마 조회 완료: id=$id" } }
+    }
+
     @Transactional
     fun createTheme(request: ThemeCreateRequestV2): ThemeCreateResponseV2 {
         log.info { "[ThemeService.createTheme] 테마 생성 시작: name=${request.name}" }