Make "Get IIIF manifest" more intuitive

This looks and behaves like a link, but rather than clicking it, users should copy the URL and paste it into a Mirador viewer. A few possible modifications that might make this more intuitive:

- [ ] Handle the click by actually copying the URL to the clipboard, rather than by opening the URL in a browser tab
- [ ] Rename it to "Copy IIIF manifest URL"
- [ ] Add a clipboard icon
- [ ] Format the link as a button

Find the existing “Get IIIF manifest” link or control and trace its click behavior. Compare the current interaction with the stated Mirador workflow, then verify that the control clearly communicates how users obtain the manifest URL and that the resulting URL can be used in Mirador.

Written by the indexing model from the issue text.