Create staging folder for tagged zip exports

Author: Samuwhale

backend/services/exports.py

@@ -679,6 +679,7 @@ def _zip_resolved_file(
         zf.write(resolved.path, arcname=arcname)
         return
 
+    staging_dir.mkdir(parents=True, exist_ok=True)
     staged_path = _staged_export_path(staging_dir, resolved)
     _write_export_file(staged_path, resolved, ffmpeg)
     zf.write(staged_path, arcname=arcname)