fix: 修改文件拓展名获取逻辑

- 若无扩展名则返回空字符串

app/utils/file.ts

@@ -11,7 +11,9 @@ export function formatFileSize(sizeInBytes: number): string {
 }
 
 export function getFileExtension(filename: string): string {
-  return filename.split('.').pop() || '';
+  const lastDotIndex = filename.lastIndexOf('.');
+  if (lastDotIndex === -1) return ''; // 找不到拓展名
+  return filename.slice(lastDotIndex + 1);
 }
 
 export function formatFileExtension(ext: string): string {