Fix: Blog carousel and multi-author support

This commit addresses a regression where the 'latest posts' carousel was empty. This was caused by a recent change to support multiple authors, where the `authorId` field was replaced with `authorIds`.

The carousel has been updated to check for both `authorId` and `authorIds` to ensure all posts are displayed correctly.

This also includes the initial multi-author support changes:
- The `layouts/partials/blog-meta.html` template is updated to handle an `authorIds` array in the front matter. It maintains backward compatibility with the old `authorId` field.
- All existing blog posts have been migrated to use the new `authorIds` field.

Author: google-labs-jules[bot]

layouts/partials/blog-carousel.html

@@ -2,7 +2,7 @@
   <div class="carousel-inner">
     {{ $posts := where .Site.Pages "Section" "blog" }}
     {{ range $index, $page := $posts }}
-    {{ if .Params.authorId }}
+    {{ if or (isset .Params "authorId") (isset .Params "authorIds") }}
     <div class="carousel-item {{ if eq $index 0 }}active{{ end }}">
       <div class="card">
         <div class="card-body card-body-shadow">