Phase 6: rules editor + unsubscribe detection (AUD-72)

- FR-11 rules editor: plain-text area at /rules, saved and versioned
  (SaveRules appends a version; restore re-saves an old version), parse
  errors surfaced, one-click re-classify. The reply model now reads the
  rules document too (FR-11).
- FR-7 unsubscribe: parse and store List-Unsubscribe / List-Unsubscribe-Post
  (migration v6), detect email and web links (internal/unsubscribe), a
  domain-level ignore list, and an explicit record of what was marked. No
  code path contacts an unsubscribe link; acting on one needs Sam's approval.
- Migration v6 is additive; unsubscribe gains url/updated_at.
- Tests: detector, parser, store migration/records/candidates, rules editor,
  unsubscribe handlers, message-detail rendering.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/store/classify.go

@@ -159,3 +159,51 @@ func (s *Store) SaveRules(ctx context.Context, text string) (int, error) {
 	}
 	return next, nil
 }
+
+// RuleVersion is one saved rules revision, for the version list in the editor
+// (FR-11).
+type RuleVersion struct {
+	ID        int64
+	Version   int
+	Text      string
+	CreatedAt string
+}
+
+// RulesVersions returns saved rules revisions, newest first.
+func (s *Store) RulesVersions(ctx context.Context, limit int) ([]RuleVersion, error) {
+	if limit < 1 {
+		limit = 20
+	}
+	rows, err := s.db.QueryContext(ctx,
+		`SELECT id, version, text, created_at FROM rules ORDER BY version DESC LIMIT ?`, limit)
+	if err != nil {
+		return nil, fmt.Errorf("list rules versions: %w", err)
+	}
+	defer rows.Close()
+	var out []RuleVersion
+	for rows.Next() {
+		var v RuleVersion
+		if err := rows.Scan(&v.ID, &v.Version, &v.Text, &v.CreatedAt); err != nil {
+			return nil, fmt.Errorf("scan rules version: %w", err)
+		}
+		out = append(out, v)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("list rules versions: %w", err)
+	}
+	return out, nil
+}
+
+// RuleByVersion returns the text of one saved rules revision. ok is false when
+// the version does not exist.
+func (s *Store) RuleByVersion(ctx context.Context, version int) (string, bool, error) {
+	var text string
+	err := s.db.QueryRowContext(ctx, `SELECT text FROM rules WHERE version = ?`, version).Scan(&text)
+	if errors.Is(err, sql.ErrNoRows) {
+		return "", false, nil
+	}
+	if err != nil {
+		return "", false, fmt.Errorf("read rules version %d: %w", version, err)
+	}
+	return text, true, nil
+}