Broken HTML signature Mail 5.1.3 links and images not working

Steps to reproduce

1. go to an HTML editor that convert HTML source to a visual signature (as badly Mail doesn't support HTML source edit or input); you can use https://htmledit.squarefree.com/ or https://onlinehtmleditor.dev/

The HTML source of the signature you need to test is:

<a href="https://demo.livehelperchat.com" target="_blank" rel="noopener noreferrer">
  <img 
    src="https://demo.livehelperchat.com/site_admin/restapi/onlineimage?&online=I'm%20online&offline=I'm%20offline&w=200" 
    alt="Chatta con noi"
    style="display: block; margin: 0 auto; cursor: pointer;" />
</a>

The result will be an image that is clickable (that has a link that open if clicked):

2. copy this signature into Mail app
3. Send an email and you will see that the image has no link and maybe is also not aligned on the center
   Also if you try to insert a link in this image in the editor on Mail signature editor page you can't

Expected behavior

Pasted signature should work as expected as in the external editor so the result for the example above should be an image that is centred, clickable and that open a link

Actual behavior

In the signature editor if you paste the signature above you cannot insert a link because all editor button are disabled.

So two issues: pasted HTML signature is pasted broken with the image that miss a link.
Also if is showed centred will be not centred when email is sent and link is missing. Also in the editor is no more possibile use the link button to add a link as showed in the above screenshot

Mail app version

5.1.3

Nextcloud version

3.1.0.5

Mailserver or service

personal one custom domain

Operating system

Ubuntu 22.04.5 LTS

PHP engine version

Other

Nextcloud memory caching

No response

Web server

Other

Database

MariaDB

Additional info

https://github.com/nextcloud/mail/issues/11260#issuecomment-2965552441

Start at the Mail signature editor and reproduce the supplied HTML signature with its linked image. Compare the saved signature and the resulting sent email, checking whether the image link, centering, and editor link controls match the expected behavior; done means the pasted signature remains clickable and centered when sent.