feat: notifications say what changed and alert once: a grouped notice names the tracks, grows without re-alerting, and a phone pile lists its titles (M542 #6146-#6151)

- An update to a grouped notice keeps its arrival time and email state, so the
  phone and the email no longer go off again each time it grows.
- Notices carry the names of what changed (newest ten), shown as three and
  "and N more": tracks still missing after the scan's move/replacement fold,
  duplicate groups new to a sweep, songs merged automatically, and the track
  and listener a playback error was for.
- Duplicates found counts only the groups new to that sweep; playback errors
  count reports, not the unresolved total.
- A scan failure says what stopped and links to Admin > Library.
- Android: a pile of more than three alerts lists the newest five titles.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/dbq/duplicates.sql.go

@@ -27,24 +27,6 @@ func (q *Queries) AddDuplicateGroupMember(ctx context.Context, arg AddDuplicateG
 	return err
 }
 
-const countDuplicateGroupsDetectedSince = `-- name: CountDuplicateGroupsDetectedSince :one
-SELECT count(*)::bigint
-  FROM duplicate_groups
- WHERE status = 'pending'
-   AND detected_at >= $1
-`
-
-// Pending proposals first made at or after `since`: what a sweep that started
-// then found for the first time. A refreshed proposal keeps its detected_at,
-// so a sweep that only re-finds known groups counts none (M489: admins are
-// told about new duplicates, not reminded of the same ones every sweep).
-func (q *Queries) CountDuplicateGroupsDetectedSince(ctx context.Context, since pgtype.Timestamptz) (int64, error) {
-	row := q.db.QueryRow(ctx, countDuplicateGroupsDetectedSince, since)
-	var column_1 int64
-	err := row.Scan(&column_1)
-	return column_1, err
-}
-
 const countPendingDuplicateGroups = `-- name: CountPendingDuplicateGroups :one
 SELECT count(*)::bigint
   FROM duplicate_groups g
@@ -311,6 +293,58 @@ func (q *Queries) ListDuplicateCandidates(ctx context.Context, arg ListDuplicate
 	return items, nil
 }
 
+const listDuplicateGroupsDetectedSince = `-- name: ListDuplicateGroupsDetectedSince :many
+SELECT ar.name AS artist_name, t.title, count(*) OVER ()::bigint AS total
+  FROM duplicate_groups g
+  JOIN LATERAL (SELECT m.track_id
+                  FROM duplicate_group_members m
+                 WHERE m.group_id = g.id
+                 ORDER BY m.track_id
+                 LIMIT 1) one ON true
+  JOIN tracks t ON t.id = one.track_id
+  JOIN artists ar ON ar.id = t.artist_id
+ WHERE g.status = 'pending'
+   AND g.detected_at >= $1
+ ORDER BY g.detected_at DESC, g.id
+ LIMIT $2
+`
+
+type ListDuplicateGroupsDetectedSinceParams struct {
+	Since pgtype.Timestamptz
+	N     int32
+}
+
+type ListDuplicateGroupsDetectedSinceRow struct {
+	ArtistName string
+	Title      string
+	Total      int64
+}
+
+// Pending proposals first made at or after `since`: what a sweep that started
+// then found for the first time, each named by one of its songs, and `total`
+// of them however many are listed. A refreshed proposal keeps its detected_at,
+// so a sweep that only re-finds known groups lists none (M489: admins are told
+// about new duplicates, not reminded of the same ones every sweep).
+func (q *Queries) ListDuplicateGroupsDetectedSince(ctx context.Context, arg ListDuplicateGroupsDetectedSinceParams) ([]ListDuplicateGroupsDetectedSinceRow, error) {
+	rows, err := q.db.Query(ctx, listDuplicateGroupsDetectedSince, arg.Since, arg.N)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListDuplicateGroupsDetectedSinceRow
+	for rows.Next() {
+		var i ListDuplicateGroupsDetectedSinceRow
+		if err := rows.Scan(&i.ArtistName, &i.Title, &i.Total); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const listDuplicateGroupsForResolve = `-- name: ListDuplicateGroupsForResolve :many
 SELECT g.id                  AS group_id,
        g.tier,