Fix account tags not being saved correctly (#11507)

* Fix account tags not being saved correctly

Regression from f371b32

Fix Tag#discoverable not returning tags where listable is nil instead of true

Add notice when saving hashtags in admin UI

Change public hashtag and directory pages to return 404 for forbidden tags

* Remove unused locale string

app/controllers/directories_controller.rb

@@ -25,7 +25,7 @@ class DirectoriesController < ApplicationController
   end
 
   def set_tag
-    @tag = Tag.discoverable.find_by!(name: params[:id].downcase)
+    @tag = Tag.discoverable.find_normalized!(params[:id])
   end
 
   def set_tags