Curation v2 step 5: deep assessment, utility, diversified shortlist

assess.rs replaces score.rs (DEEP_INSTRUCTIONS, representative sample
with [BEGINNING]/[MIDDLE]/[END], facets, cached deep rows with --rescore
bypass), rank.rs adds the utility blend over present signals with gate
ramps and the leader-clustered shortlist (cap 2 → 3 → uncapped, protected
top-N, exploration reserve), editor.rs replaces select.rs with the §13
rendering and utility-ordered fallbacks. ScoredArticle is gone; Candidate
is the only flow type. deep_batch_size replaces score_batch_size.

Started by Codex (cut off by its usage limit mid-verification) and
finished by a Claude agent from docs/plans/curation-v2-briefs/step5.md;
reviewed against plan §12–§13.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A1rCLQeKBgnBo3oTgHuTMe

src/curate/prefilter.rs

@@ -125,9 +125,7 @@ pub fn roundup_penalty(title: &str) -> f64 {
 #[cfg(test)]
 pub(crate) mod tests {
     use super::*;
-    use crate::types::{
-        ArticleId, ExtractMethod, FeedId, SocialRef, SocialSource, SourceKind, SourceRef,
-    };
+    use crate::types::{ArticleId, ExtractMethod, SocialRef, SocialSource, SourceKind, SourceRef};
     use jiff::Timestamp;
 
     pub(crate) fn ts() -> Timestamp {
@@ -180,17 +178,6 @@ pub(crate) mod tests {
         article
     }
 
-    pub(crate) fn via(mut article: Article, kind: SourceKind, feed_id: FeedId) -> Article {
-        article.sources.push(SourceRef {
-            entry_id: article.best_entry_id,
-            feed_id,
-            feed_title: format!("{kind:?} feed"),
-            category: None,
-            kind,
-        });
-        article
-    }
-
     #[test]
     fn text_heuristic_has_only_text_terms() {
         let quiet = article(1, "An essay", 1200);