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

@@ -809,16 +809,21 @@ 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) {
-            String relativePath = knowledgeItem.getContent();
-            if (StringUtils.isNotBlank(relativePath)) {
-                try {
-                    Path filePath = resolveKnowledgeItemStoragePath(relativePath);
-                    deleteFileQuietly(filePath);
-                } catch (Exception e) {
-                    log.warn("delete knowledge item file error, itemId: {}, path: {}", knowledgeItem.getId(), relativePath, e);
-                }
+        if (sourceType != KnowledgeSourceType.FILE_UPLOAD && sourceType != KnowledgeSourceType.MANUAL) {
+            return;
+        }
+
+        String relativePath = knowledgeItem.getContent();
+        if (StringUtils.isNotBlank(relativePath)) {
+            try {
+                Path filePath = resolveKnowledgeItemStoragePath(relativePath);
+                deleteFileQuietly(filePath);
+            } catch (Exception e) {
+                log.warn("delete knowledge item file error, itemId: {}, path: {}", knowledgeItem.getId(), relativePath, e);
             }
         }
     }