Tools that combine several files into a single PDF used the upload
order as the page order, with no way to change it short of clearing
and re-adding files. Each file row now has a drag handle, and the
new order is used when the PDF is built.
Applies to the JPG, PNG, WebP, BMP, HEIC, SVG, TIFF, Image and TXT
to PDF tools. The shared logic lives in utils/sortable-file-list.ts
(built on the existing sortablejs dependency) instead of being
duplicated per page.