fix(knowledge): 优化知识项文件删除逻辑

- 添加内容类型检查，仅处理文件类型的知识项
- 修改源类型判断条件，提前返回非文件上传和手动创建的类型
- 保持原有的文件路径解析和删除操作逻辑
- 维持异常处理和日志记录功能

backend/services/data-management-service/src/main/java/com/datamate/datamanagement/application/KnowledgeItemApplicationService.java

@@ -809,8 +809,14 @@ public class KnowledgeItemApplicationService {
         if (knowledgeItem == null) {
             return;
         }
+        if (knowledgeItem.getContentType() != KnowledgeContentType.FILE) {
+            return;
+        }
         KnowledgeSourceType sourceType = knowledgeItem.getSourceType();
-        if (sourceType == KnowledgeSourceType.FILE_UPLOAD || sourceType == KnowledgeSourceType.MANUAL) {
+        if (sourceType != KnowledgeSourceType.FILE_UPLOAD && sourceType != KnowledgeSourceType.MANUAL) {
+            return;
+        }
+
         String relativePath = knowledgeItem.getContent();
         if (StringUtils.isNotBlank(relativePath)) {
             try {
@@ -821,7 +827,6 @@ public class KnowledgeItemApplicationService {
             }
         }
     }
-    }
 
     private String resolveOriginalFileName(MultipartFile file) {
         String originalName = file.getOriginalFilename();