openGalleryModal interpolated width, height and file_size (stored from a
POST body, so possibly strings) straight into data-caption and the card
text. showWorkflowData wrote JSON.stringify(workflow) raw into a blank
same-origin window, so a workflow containing </pre><script> ran. Both now
go through ImageHelpers (new pure module, node:test covered); a string
file_size no longer reaches formatFileSize's toFixed either, and a blocked
popup shows a notice instead of throwing.