Make link names unique and keep comment avatars in the same tab

[MaggieCabrera]

Description

Builds on #93 by @noruzzamans. Its commit is included here, rebased on trunk. Fixes #47 and is part of #44.

• Post dates and comment dates are no longer links, so posts or comments from the same day don't share a link name anymore. That now includes archive-lead and page-blog-home, which landed after Fix ambiguous link texts by removing redundant post date links and adding screen reader text to comments CTA #93. Removing the links follows what we agreed on in Fix: Add unique accessible names to post-date and Comments CTA links #54.
• Screen readers hear the post title in the comments call to action, like "Join the conversation on Hello world!". The visible text stays the same.
• Comment avatars open the commenter's site in the same tab. The new-tab warning only lived in an aria-label, and the accessibility-ready guideline asks for a warning sighted visitors can see too.

Screenshots

Testing Instructions

1. Import the accessibility test content, or add a few posts on the same day and a post with comments.
2. On the blog home, a category archive and the search results, check that dates are plain text.
3. Inspect a "Join the conversation" or "Be the first to comment" link in the browser's accessibility tree. Its name ends with the post title.
4. Open "Template: Comments". Comment dates are plain text, and a commenter's avatar opens their site in the same tab.
5. In the Site Editor, open Index and Single Posts. There are no block recovery warnings.

Checked on the front end, in the Site Editor, and with the Blue Hour and Evening variations.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5.5
Used for: The accessibility audit, rebasing #93 onto trunk, the follow-up changes and this description.

🤖 Generated with Claude Code