Remove SafeText from url so it can be escaped

[Providence-o]

Fixes #2131

format_html marks the url string as a SafeText which prevents it from being escaped when the html is rendered

[thibaudcolas]

@Providence-o thank you for giving this a go! This fixes #2131 but reintroduces another issue, which is that alt_text needs to have some escaping done still, at least for double quotes.

Here is what arrives in my clipboard if I use the "Raw HTML" copy button for an image with alt text Green events "tools":

<img src="/m/blog/images/2025/10/green_events_tools.png" alt="Green events "tools"">

This is now invalid HTML since there are double quotes inside alt. Instead, we would want:

<img src="/m/blog/images/2025/10/green_events_tools.png" alt="Green events &quot;tools&quot;">