- check_original_declaration: replace the original checkbox with the
'来源转载' (repost) declaration flow: open the declaration picker, select
'来源转载', fill the media name, confirm. Falls back to JS click when the
element text is wrapped in non-interactive spans
- set_thumbnail: switch to the '上传封面' tab and target the upload-wrapper
file input instead of the cover-plugin-preview selector; skip gracefully on
failure and let the video first frame be used