Show who signs a post and its tags, and read the blog by tag

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -265,6 +265,11 @@ any page. That category has to exist with the slug `blog` in every language
 - `/blog` (`/en/blog`, `/ca/blog`) lists them newest first.
 - A post shows its date and leads back to the blog; its structured data is a
   `BlogPosting`.
+- A post shows who signs it (`byline`, linked to their profile) and its tags,
+  each linking to `/blog?tag=…`. The blog offers the tags in use as a row of
+  links and narrows to one with `?tag=` — plain links, so a tag's listing can
+  be shared and works before any script runs. Tags and bylines are set in the
+  panel.
 - `/blog/rss.xml?lang=xx` is the feed, one per language, announced in `<head>`.
 - Once there is a post, the blog is in the header menu (desktop and mobile)
   and the landing shows the three latest under "Novedades"; the footer links