Keep the publication an article's page declares

Readability already reads og:site_name and JSON-LD publisher.name; carry
that through Page and Extracted and store it in articles.publication, the
same way the page byline is kept. `publication_label` is what the readers
will see after the feed name: the site name, else the domain, and nothing
when it would only repeat the feed's own title.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YWmCpUojfHXhSZ2129Z7Nv

src/dedupe.rs

@@ -409,6 +409,7 @@ fn build_article(members: Vec<(Entry, String)>, feed_urls: &FeedUrls) -> Article
         first_seen,
         url: best_entry.url.clone(),
         author,
+        publication: None,
         feed_id: best_entry.feed_id,
         feed_title: best_entry
             .feed_title