chore: performance fixes for response rate calculation

app/controllers/overview_controller.rb

@@ -37,6 +37,6 @@ class OverviewController < SqmApplicationController
   end
 
   def categories
-    @categories ||= Category.sorted.includes(%i[measures admin_data_items subcategories])
+    @categories ||= Category.sorted.includes(%i[measures scales admin_data_items subcategories])
   end
 end

app/models/category.rb

@@ -9,4 +9,5 @@ class Category < ActiveRecord::Base
   has_many :subcategories
   has_many :measures, through: :subcategories
   has_many :admin_data_items, through: :measures
+  has_many :scales, through: :subcategories
 end