FEATURE: Conditionally force optimized category style (#29473)

The `categories_only_optimized` category page style has been introduced
in commit d37a0d401c. This commit makes
sure that style is enforced for users who can see over 1000 categories
in order to keep `/categories` page functional.

app/models/category_list.rb

@@ -4,6 +4,9 @@ class CategoryList
   CATEGORIES_PER_PAGE = 20
   SUBCATEGORIES_PER_CATEGORY = 5
 
+  # Maximum number of categories before the optimized category page style is enforced
+  MAX_UNOPTIMIZED_CATEGORIES = 1000
+
   include ActiveModel::Serialization
 
   cattr_accessor :preloaded_topic_custom_fields
@@ -139,9 +142,14 @@ class CategoryList
       query = query.where(parent_category_id: @options[:parent_category_id])
     end
 
+    style =
+      if Category.secured(@guardian).count > MAX_UNOPTIMIZED_CATEGORIES
+        "categories_only_optimized"
+      else
+        SiteSetting.desktop_category_page_style
+      end
     page = [1, @options[:page].to_i].max
-    if SiteSetting.desktop_category_page_style == "categories_only_optimized" ||
-         @guardian.can_lazy_load_categories?
+    if style == "categories_only_optimized" || @guardian.can_lazy_load_categories?
       query = query.limit(CATEGORIES_PER_PAGE).offset((page - 1) * CATEGORIES_PER_PAGE)
     elsif page > 1
       # Pagination is supported only when lazy load is enabled. If it is not,