Special characters in anchor text cause truncation

Problem/Motivation

When a mailto: link's visible text contains an HTML special character (e.g. <a href="mailto:x@example.com">Life & Work Connections</a>)ObfuscateEmail::process() silently deletes the link's text content. The anchor tag survives, but ends up empty.

<!-- before -->                                                                                                                                                                                                        
<a href="mailto:x@example.com">Life & Work Connections</a>                                                                                                                                                             
                                                                                                                                                                                                                         
<!-- after obfuscate_email filter runs -->                                                                                                                                                                             
<a href="#" data-mail-to="..." data-replace-inner="@email"></a>

Steps to reproduce

1. Enable the "Obfuscate Email" filter on a text format.
2. Create content with a mailto link whose visible text contains an ampersand, e.g.: <a href="mailto:test@example.com">Sales & Support</a>
3. Save and view the rendered output.
4. Observe the anchor tag is present but its inner text has been deleted.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes