Split large activity Excel prepare from chunk import and clarify errors.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/activities/activities.controller.ts

@@ -100,6 +100,19 @@ export class ActivitiesController {
     return this.excelService.preview(file);
   }
 
+  @Post('import/prepare')
+  @UseInterceptors(excelUpload)
+  importPrepare(
+    @CurrentUser() user: Actor,
+    @UploadedFile() file?: Express.Multer.File,
+    @Body('mapping') mapping?: string,
+  ) {
+    if (!file?.buffer?.length) {
+      throw new BadRequestException('فایل ارسال نشده');
+    }
+    return this.excelService.prepare(user, file, mapping);
+  }
+
   @Post('import')
   @UseInterceptors(excelUpload)
   import(