pundit: convert tags to pundit.

app/policies/tag_policy.rb

@@ -0,0 +1,15 @@
+class TagPolicy < ApplicationPolicy
+  def can_change_category?
+    user.is_admin? ||
+      (user.is_builder? && !record.is_locked? && record.post_count < 1_000) ||
+      (user.is_member? && !record.is_locked? && record.post_count < 50)
+  end
+
+  def can_lock?
+    user.is_moderator?
+  end
+
+  def permitted_attributes
+    [(:category if can_change_category?), (:is_locked if can_lock?)].compact
+  end
+end