Links in the Activity Dashboard widget can only be distinguished by color

[afercia]

In the Activity Dashboard widget, the links to the comment author and to the post are within a block of text and only use color to be distinguished from normal text.

While other links in the widget, for example the row action links and the links in the footer, can be distinguished as links by the context, the links within a block of text cannot rely on color alone.

This is a specific WCAG violation and, for what is worth, would be reported by any accessibility checker. For example, axe-core reports a violation for the rule link-in-text-block with description: Ensure links are distinguished from surrounding text in a way that does not rely on color.

These links need an additional shape. Normally it's the link underline but it may be any other shape that helps distinguish them as links.

Discovered while testing ​the experimental PR for #66015.

See screenshots:

• The highlighted links in the first screenshot are not compliant.
• An example of the entire widget with no color, where these links cannot be distinguished from the surrounding text.

In the Activity dashboard widget, the comment author and post links sit inside a sentence and are distinguished from the surrounding text by color alone, which axe-core reports as a link-in-text-block violation.

#dashboard-widgets li a removes the underline from every link inside a dashboard widget list item, including the two links in the .comment-meta sentence. This patch restores text-decoration: underline for links within .comment-meta.

The row action and footer links, which context already distinguishes as links, are unchanged.

Trac ticket: https://core.trac.wordpress.org/ticket/66017

## Use of AI Tools
AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5
Used for: Writing PR details. All changes were reviewed and validated by me.

I pushed a commit to use :not() and also to exclude the links for 'Publishing Soon' and 'Recently Published'. Screenshot before and after:

[afercia]

In 63536:

Administration: Ensure the Activity Dashboard widget links are distinguished from surrounding text.

Links within blocks of text must be distinguished in a way that does not rely on color.

Developed in ​https://github.com/WordPress/wordpress-develop/pull/13357

Props khokansardar, afercia, joedolson.
Fixes #66017.