docx-preview defaults to blob: URLs for embedded images, which DOMPurify
strips from img src (blob: isn't in its default allowed-URI list), so
figures vanished after sanitize. Switch docx-preview to useBase64URL so
images inline as data: URIs, and add ADD_DATA_URI_TAGS: ['img'] to the
DOMPurify config so those data: URIs survive sanitization. Script /
handler / javascript: stripping is unchanged.