Use grid layout for author pages (consistent with blog list page). Dletion of duplicate image.

[VanescoB]

Author pages now show posts in the same card grid as the main blog page, instead of the default Docusaurus post list.

Changes

New author page layout

• Added src/theme/Blog/Pages/BlogAuthorsPostsPage, a copy of the Docusaurus 3.10 original. It uses Docusaurus functions that aren't officially supported, so check it against upstream when upgrading Docusaurus.
• The author header (photo, name, title, social links, description, "View all authors") is now in a bordered box styled like the cards.
• Posts appear as cards. Author names are hidden on the cards because they would repeat the page's author.
• When an author has fewer than 3 posts in total, the cards stretch to fill the width: 2 posts fill the row as two columns, and 1 post takes the whole row with a taller image on desktop. This uses the author's total post count, so a page 2 with a single leftover post keeps the normal grid. With 3 or more posts, the layout matches the main page.

Shared card grid component

• Moved the card markup and styles from BlogListPage into a new src/components/BlogPostGrid component. The main page and the author pages both use it.

Card improvements (affect both pages)

• Titles, images and tags use Docusaurus <Link> instead of <a href>, so clicks no longer reload the whole page.
• The card image now opens the post. It's hidden from keyboard and screen readers because the title links to the same place.
• Images have empty alt text (screen readers no longer read the title twice) and load only when they're about to scroll into view.
• The hover shadow uses the theme colour instead of a leftover cyan.
• Dates are shown in UTC, so readers in western time zones no longer see the previous day.