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/server.rs

@@ -972,6 +972,7 @@ mod tests {
                 first_seen: ts("2026-08-15T05:30:00Z"),
                 url: "https://example.com/1".into(),
                 author: None,
+                publication: None,
                 feed_id: 7,
                 feed_title: "Hacker News".into(),
                 category: None,