Simplify related articles: shared article header, ids only, no job

- Both article pages render one `_article_head.html` partial from an
  `ArticleHead` built by a single constructor instead of two copies.
- `related::for_article` returns ids; the cosine stays stored for tuning.
- Title keys travel with each candidate, dropping the side map.
- Drop the `related-refresh` dashboard job: the backfill is a one-off and
  `features related` covers it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AeJmv3WED4w8S3GV7mMjS7

src/web/issue.rs

@@ -943,19 +943,8 @@ struct ArticleLink {
 struct ArticleTemplate {
     page: Page,
     toc: Toc,
-    title: String,
-    source_url: String,
-    byline: Option<String>,
-    source: Source,
-    meta_line: String,
-    social_line: Option<String>,
-    understanding: chapters::Understanding,
-    summary: Option<String>,
-    excerpt_only: bool,
-    body_html: String,
+    head: ArticleHead,
     discussion_html: Option<String>,
-    read_online_url: String,
-    dashboard_href: String,
     rating: Option<RatingWidget>,
     previous: Option<ArticleLink>,
     next: Option<ArticleLink>,
@@ -969,18 +958,50 @@ struct ArticleTemplate {
 #[template(path = "article_standalone.html")]
 struct StandaloneArticleTemplate {
     page: Page,
+    head: ArticleHead,
+}
+
+/// What `_article_head.html` renders (header and body) plus the footer links
+/// both article pages share.
+struct ArticleHead {
     title: String,
     source_url: String,
     byline: Option<String>,
     source: Source,
     meta_line: String,
     social_line: Option<String>,
+    /// Issue-only: empty and `None` on the standalone page.
+    understanding: chapters::Understanding,
+    summary: Option<String>,
     excerpt_only: bool,
     body_html: String,
     read_online_url: String,
     dashboard_href: String,
 }
 
+impl ArticleHead {
+    fn new(article: &Article, config: &Config, is_admin: bool) -> Self {
+        Self {
+            title: article.title.clone(),
+            source_url: article.canonical_url.clone(),
+            byline: article.author.as_ref().map(|author| format!("By {author}")),
+            source: Source::new(article, config, is_admin),
+            meta_line: format!(
+                "{} words · ~{} min read",
+                thousands(article.word_count),
+                article.reading_minutes()
+            ),
+            social_line: chapters::social_line(&article.social),
+            understanding: chapters::Understanding::default(),
+            summary: None,
+            excerpt_only: article.excerpt_only,
+            body_html: prepare_body(&article.content_html),
+            read_online_url: article.url.clone(),
+            dashboard_href: format!("/dashboard/articles/{}", article.id),
+        }
+    }
+}
+
 /// One entry of the "Related" list under an issue article.
 #[derive(Debug)]
 struct RelatedView {
@@ -1150,26 +1171,15 @@ pub async fn article(
     Ok(Html(ArticleTemplate {
         page,
         toc,
-        title: article.title.clone(),
-        source_url: article.canonical_url.clone(),
-        byline: article.author.as_ref().map(|author| format!("By {author}")),
-        source: Source::new(article, &config, is_admin),
-        meta_line: format!(
-            "{} words · ~{} min read",
-            thousands(article.word_count),
-            article.reading_minutes()
-        ),
-        social_line: chapters::social_line(&article.social),
-        understanding: chapters::understanding(pick),
-        summary: summary_for(&view.issue, pick).map(str::to_string),
-        excerpt_only: article.excerpt_only,
-        body_html: prepare_body(&article.content_html),
+        head: ArticleHead {
+            understanding: chapters::understanding(pick),
+            summary: summary_for(&view.issue, pick).map(str::to_string),
+            ..ArticleHead::new(article, &config, is_admin)
+        },
         discussion_html: pick
             .discussion
             .as_ref()
             .map(|discussion| crate::comments::render_xhtml(discussion, &article.title)),
-        read_online_url: article.url.clone(),
-        dashboard_href: format!("/dashboard/articles/{}", article.id),
         rating: is_admin.then(|| {
             RatingWidget::for_issue(
                 article.id,
@@ -1217,20 +1227,7 @@ pub async fn standalone(
     page.flash = take_flash(&session).await?;
     Ok(Html(StandaloneArticleTemplate {
         page,
-        title: article.title.clone(),
-        source_url: article.canonical_url.clone(),
-        byline: article.author.as_ref().map(|author| format!("By {author}")),
-        source: Source::new(&article, &config, is_admin),
-        meta_line: format!(
-            "{} words · ~{} min read",
-            thousands(article.word_count),
-            article.reading_minutes()
-        ),
-        social_line: chapters::social_line(&article.social),
-        excerpt_only: article.excerpt_only,
-        body_html: prepare_body(&article.content_html),
-        read_online_url: article.url.clone(),
-        dashboard_href: format!("/dashboard/articles/{}", article.id),
+        head: ArticleHead::new(&article, &config, is_admin),
     })
     .into_response())
 }
@@ -1244,18 +1241,17 @@ async fn related_views(
     date: Date,
     article_id: ArticleId,
 ) -> anyhow::Result<Vec<RelatedView>> {
-    let links = crate::related::for_article(db, date, article_id).await?;
-    if links.is_empty() {
+    let ids = crate::related::for_article(db, date, article_id).await?;
+    if ids.is_empty() {
         return Ok(Vec::new());
     }
-    let ids: Vec<ArticleId> = links.iter().map(|link| link.article_id).collect();
     let articles = db.get_articles(&ids).await?;
     let issues = crate::related::latest_issues(db, &ids).await?;
-    Ok(links
+    Ok(ids
         .iter()
-        .filter_map(|link| {
-            let article = articles.get(&link.article_id)?;
-            let href = match issues.get(&link.article_id) {
+        .filter_map(|id| {
+            let article = articles.get(id)?;
+            let href = match issues.get(id) {
                 Some(date) => article_href(*date, article.id),
                 None => standalone_href(article.id),
             };