feat: 支持知识库导入 PPTX 与 XLSX 文档

- 打通 Office 文档桥接解析、解析进度承接与图片引用改写

- 落地 PPTX 按页分块、XLSX 行窗口分块以及预览与检索渲染闭环

easyflow-ui-admin/app/src/views/ai/documentCollection/KnowledgeSearch.vue

@@ -21,6 +21,8 @@ type RetrievalMode = 'HYBRID' | 'KEYWORD' | 'VECTOR';
 interface SearchResultItem {
   sorting: number;
   content: string;
+  renderMarkdown?: string;
+  sourceFileName?: string;
   score?: number;
   hitSource?: 'BOTH' | 'KEYWORD' | 'VECTOR';
   vectorScore?: number;