Properly localise FormsHelper helpers

These should use `full_messages` to get the field names from i18n,
rather than just humanizing the field name.

app/helpers/forms_helper.rb

@@ -2,15 +2,15 @@ module FormsHelper
   def error_items(record, field)
     return unless record.errors[field].any?
 
-    record.errors[field].map do |error|
-      { text: "#{field.to_s.humanize} #{error}" }
+    record.errors.full_messages_for(field).map do |error|
+      { text: error }
     end
   end
 
   def error_summary_items(record)
     record.errors.map do |error|
       {
-        text: "#{error.attribute.to_s.humanize} #{error.message}",
+        text: error.full_message,
         href: "##{record.class.name.underscore}_#{error.attribute}",
       }
     end