Fixes#1680
The HTML2Text class was ignoring the <base> tag, causing relative links
to be resolved against the page URL instead of the base URL specified
in the <base href="..."> attribute.
Added <base> tag handling in both HTML2Text and CustomHTML2Text to update
self.baseurl when the tag is encountered, ensuring proper link resolution
according to HTML standards.
Co-Authored-By: Claude <noreply@anthropic.com>
2016d669a9