fix(who): exclude self-assigned reviewers from file-change reviewer signal

Signal 4 (mr_reviewers + mr_file_changes) was missing the self-review
exclusion that signal 1 (DiffNote reviewer) already had. An MR author
listed as their own reviewer would be double-counted as both author
and reviewer, inflating their score.

Also removes redundant SELECT DISTINCT from signal 2 (GROUP BY
already ensures uniqueness).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/commands/who.rs

@@ -568,7 +568,7 @@ fn query_expert(
             UNION ALL
 
             -- 2. DiffNote MR author
-            SELECT DISTINCT
+            SELECT
                 m.author_username AS username,
                 'diffnote_author' AS signal,
                 m.id AS mr_id,
@@ -616,6 +616,7 @@ fn query_expert(
             JOIN merge_requests m ON fc.merge_request_id = m.id
             JOIN mr_reviewers r ON r.merge_request_id = m.id
             WHERE r.username IS NOT NULL
+              AND (m.author_username IS NULL OR r.username != m.author_username)
               AND m.state IN ('opened','merged')
               AND fc.new_path {path_op}
               AND m.updated_at >= ?2
@@ -1257,6 +1258,7 @@ fn query_overlap(
             JOIN projects p ON m.project_id = p.id
             JOIN mr_reviewers r ON r.merge_request_id = m.id
             WHERE r.username IS NOT NULL
+              AND (m.author_username IS NULL OR r.username != m.author_username)
               AND m.state IN ('opened','merged')
               AND fc.new_path {path_op}
               AND m.updated_at >= ?2
@@ -2845,4 +2847,53 @@ mod tests {
         assert_eq!(pq.value, "src/Dockerfile");
         assert!(!pq.is_prefix);
     }
+
+    #[test]
+    fn test_expert_excludes_self_assigned_reviewer() {
+        // MR author listed in mr_reviewers for their own MR should NOT be
+        // counted as a reviewer (same principle as DiffNote self-review exclusion)
+        let conn = setup_test_db();
+        insert_project(&conn, 1, "team/backend");
+        insert_mr(&conn, 1, 1, 100, "author_a", "merged");
+        insert_file_change(&conn, 1, 1, "src/auth/login.rs", "modified");
+        // author_a is self-assigned as reviewer
+        insert_reviewer(&conn, 1, "author_a");
+        // real_reviewer is also assigned
+        insert_reviewer(&conn, 1, "real_reviewer");
+
+        let result = query_expert(&conn, "src/auth/login.rs", None, 0, 20).unwrap();
+
+        // author_a should appear as author only, not reviewer
+        let author = result
+            .experts
+            .iter()
+            .find(|e| e.username == "author_a")
+            .unwrap();
+        assert_eq!(author.review_mr_count, 0);
+        assert!(author.author_mr_count > 0);
+
+        // real_reviewer should appear as reviewer
+        let reviewer = result
+            .experts
+            .iter()
+            .find(|e| e.username == "real_reviewer")
+            .unwrap();
+        assert!(reviewer.review_mr_count > 0);
+    }
+
+    #[test]
+    fn test_overlap_excludes_self_assigned_reviewer() {
+        // Same self-review exclusion for overlap mode via file changes
+        let conn = setup_test_db();
+        insert_project(&conn, 1, "team/backend");
+        insert_mr(&conn, 1, 1, 100, "author_a", "merged");
+        insert_file_change(&conn, 1, 1, "src/auth/login.rs", "modified");
+        insert_reviewer(&conn, 1, "author_a"); // self-assigned
+
+        let result = query_overlap(&conn, "src/auth/", None, 0, 20).unwrap();
+        let user = result.users.iter().find(|u| u.username == "author_a");
+        // Should appear (as author) but NOT have reviewer touch count
+        assert!(user.is_some());
+        assert_eq!(user.unwrap().review_touch_count, 0);
+    }
 }