Add an AI slop verdict that downrates the author's future articles

A fourth explicit verdict, "AI slop" (Vote::Slop, label `slop`), joins the
rating widget on the web, the EPUB footer links, the /r/ confirmation page,
the CLI, imports and the dashboard filters. It counts as a full negative
(curation.feedback.slop_value, -1.0) in the neighbour and affinity signals.

Beyond that, each run loads the authors whose current verdict is slop, with
no lookback, and multiplies the preliminary blend and the utility of every
candidate by that author by 1 - curation.ranking.slop_author_penalty (0.75),
so they sink before triage. The flag is recorded in signals_json, shown by
`explain` and the dashboard signals table, and the confirmation names the
author (or says no author is known, in which case only the rating applies).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VXYGBPoHZSDSfE5WcJ9bvj

src/config.rs

@@ -468,6 +468,10 @@ pub struct RankingConfig {
     pub knn_full: usize,
     pub feed_floor: usize,
     pub feed_full: usize,
+    /// Fraction of the preliminary blend and the utility removed from any
+    /// candidate whose author has a current *AI slop* verdict (§9.3). `1.0`
+    /// zeroes such candidates; `0.0` disables the penalty.
+    pub slop_author_penalty: f64,
     pub semantic_min_words: i64,
     pub exploration_slots: usize,
     pub embedding_retention_days: i64,
@@ -492,6 +496,7 @@ impl Default for RankingConfig {
             knn_full: 25,
             feed_floor: 15,
             feed_full: 40,
+            slop_author_penalty: 0.75,
             semantic_min_words: 300,
             exploration_slots: 5,
             embedding_retention_days: 120,
@@ -603,6 +608,9 @@ pub struct FeedbackConfig {
     pub loved_value: f64,
     pub good_value: f64,
     pub not_for_me_value: f64,
+    /// Weight of an *AI slop* verdict. The author penalty is separate
+    /// (`ranking.slop_author_penalty`).
+    pub slop_value: f64,
     pub verdicts_in_prompt: usize,
 }
 
@@ -612,6 +620,7 @@ impl Default for FeedbackConfig {
             loved_value: 1.0,
             good_value: 0.35,
             not_for_me_value: -1.0,
+            slop_value: -1.0,
             verdicts_in_prompt: 60,
         }
     }
@@ -1180,6 +1189,11 @@ impl Config {
                 "curation.ranking *_full must be > *_floor >= 0".into(),
             ));
         }
+        if !(0.0..=1.0).contains(&ranking.slop_author_penalty) {
+            return Err(ConfigError::Invalid(
+                "curation.ranking.slop_author_penalty must be between 0 and 1".into(),
+            ));
+        }
         if !(0.0..=1.0).contains(&ranking.diversity.cluster_threshold) {
             return Err(ConfigError::Invalid(
                 "curation.ranking.diversity.cluster_threshold must be between 0 and 1".into(),
@@ -1438,6 +1452,8 @@ mod tests {
         assert_eq!(c.curation.recent_rejection_floor, 3.0);
         assert_eq!(c.profile_path, PathBuf::from("data/profile.md"));
         assert_eq!(c.curation.feedback.good_value, 0.35);
+        assert_eq!(c.curation.feedback.slop_value, -1.0);
+        assert_eq!(c.curation.ranking.slop_author_penalty, 0.75);
         assert_eq!(c.curation.feedback.verdicts_in_prompt, 60);
         assert_eq!(c.xtc.format, XtcFormat::Xtch);
         assert_eq!(c.curation.sections.len(), 8);