feature: Support Link Validation for Custom <footquote> Tags in Brofix

[atigiti]

We have a plugin in the RTE that generates footnotes by adding a custom tag with a URL, resulting in the following format:

<p>
  <footquote content="https://www.google.com">
    My Link
  </footquote>
</p>

On the frontend, this is rendered as a standard link:

<a href="https://www.google.com">My Link</a>

However, we’ve found that Brofix is currently unable to detect or check links defined in this way. We suggest extending Brofix’s capabilities to support this format, so it can properly identify and validate these types of links.