feat(ai-character): 오디오 콘텐츠 관리자 계약을 보강한다

src/main/kotlin/kr/co/vividnext/sodalive/content/AudioContentService.kt

@@ -220,9 +220,6 @@ class AudioContentService(
         // request 내용 파싱
         val request = objectMapper.readValue(requestString, CreateAudioContentRequest::class.java)
 
-        // 미리듣기 시간 체크
-        validatePreviewTime(request.previewStartTime, request.previewEndTime)
-
         val releaseDate = if (request.releaseDate != null) {
             request.releaseDate.convertLocalDateTime("yyyy-MM-dd HH:mm")
                 .atZone(ZoneId.of(request.timezone))
@@ -232,11 +229,26 @@ class AudioContentService(
             LocalDateTime.now()
         }
 
+        return createAudioContent(contentFile, coverImage, request, releaseDate, member)
+    }
+
+    @Transactional
+    fun createAudioContent(
+        contentFile: MultipartFile?,
+        coverImage: MultipartFile?,
+        request: CreateAudioContentRequest,
+        releaseDate: LocalDateTime,
+        member: Member
+    ): CreateAudioContentResponse {
+        if (coverImage == null) throw SodaException(messageKey = "content.error.cover_image_required")
+
         // contentFile 체크
         if (contentFile == null) {
             throw SodaException(messageKey = "content.error.content_required")
         }
 
+        validatePreviewTime(request.previewStartTime, request.previewEndTime)
+
         // 테마 체크
         val theme = themeQueryRepository.findThemeByIdAndActive(id = request.themeId)
             ?: throw SodaException(messageKey = "content.error.invalid_theme")