fix: register IndexAsCalendar at gem-require time, not via to_prepare

lib/activeadmin_calendar.rb

@@ -1,8 +1,15 @@
 # frozen_string_literal: true
 
+# Load ActiveAdmin first so `ActiveAdmin::Views` exists by the time we
+# register the view component. AA doesn't publish a load hook for itself
+# (only `:active_admin_controller`), and `config.to_prepare` would fire
+# too late for engines that require AA resources from an initializer.
+# Sibling plugins (active_admin_sidebar, etc.) use the same pattern.
+require "activeadmin"
 require "activeadmin_calendar/version"
 
 module ActiveadminCalendar
 end
 
 require "activeadmin_calendar/engine" if defined?(Rails)
+require "activeadmin_calendar/index_as_calendar"

lib/activeadmin_calendar/engine.rb

@@ -3,9 +3,10 @@
 require "rails/engine"
 
 module ActiveadminCalendar
+  # Empty engine — kept so Propshaft / Tailwind can discover this gem's
+  # `app/assets/stylesheets` directory on AA 4. The view component
+  # itself is required eagerly from `lib/activeadmin_calendar.rb` so it
+  # is available before AA resources are loaded.
   class Engine < ::Rails::Engine
-    config.to_prepare do
-      require "activeadmin_calendar/index_as_calendar"
-    end
   end
 end