fix: Standardize file creation timestamp to ISO string format

Ensure consistent ISO string representation of file creation timestamps in both file utility and knowledge content upload

src/main/utils/file.ts

@@ -45,7 +45,7 @@ export function getAllFiles(dirPath: string, arrayOfFiles: FileType[] = []): Fil
         count: 1,
         origin_name: name,
         type: fileType,
-        created_at: new Date()
+        created_at: new Date().toISOString()
       }
 
       arrayOfFiles.push(fileItem)

src/renderer/src/pages/knowledge/KnowledgeContent.tsx

@@ -100,7 +100,7 @@ const KnowledgeContent: FC<KnowledgeContentProps> = ({ selectedBase }) => {
           count: 1,
           origin_name: file.name,
           type: file.type as FileTypes,
-          created_at: new Date()
+          created_at: new Date().toISOString()
         }))
         .filter(({ ext }) => fileTypes.includes(ext))
       console.debug('[KnowledgeContent] Uploading files:', _files, files)