Enable frozen string literals.

Make all string literals immutable by default.

app/helpers/application_helper.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ApplicationHelper
   def listing_type(*fields, member_check: true, types: [:revert, :standard])
     (fields.reduce(false) { |acc, field| acc || params.dig(:search, field).present? } && (!member_check || CurrentUser.is_member?) ? types[0] : types[1])