Presentation’s PDF exports break some external links

### Description

When exporting PDFs, external links are not working. The behaviour of the links depends on the PDF viewer.

A minimal example can be found [here](https://cryptpad.fr/presentation/#/2/presentation/view/5p-KC95QI7NJCtzHfVUWN0aUT7MpDQRnlDknmyqpU0w/) with the resulting [PDF](https://github.com/user-attachments/files/21014572/Link-Export-Bug.pdf).

You can notice in the CryptPad presentation app that `Ctrl + Left Mouse Button` gives you the website of the CryptPad project on both links.

Now, if you export it, you can realise that, on the resulting PDF:
- In firefox, only the second link is clickable (and working)
- In chromium, both links are “clickable” but don’t do anything
- In evince, okular and zathura: both links link to an empty string

### Steps to reproduce

1. Create a presentation
2. Embed a link on a text by right clicking then “⛓️Hyperlink” and add a link
3. Add an automatic link (e.g. typing `https://cryptpad.org/` and add a space or a new line afterward)
4. Export the PDF
- Either by printing the file
- Or with `File > Export > .pdf`
5. Notice that links are broken

### Expected behavior

The links should be preserved upon exporting.

### Which operating system are you using?

Linux/BSD/UNIX

### What browsers are you seeing the problem on?

Mozilla Firefox

### Version

2025.6.0