Fix async script loading for auto-generated component packs

The recent refactor to use async: true for non-Redux pages (c0a3b59) caused
the image_example page to fail because of a timing issue between the main
bundle and auto-generated component packs.

The dummy app uses auto_load_bundle with components_subdirectory = "startup",
which auto-generates packs for components like ImageExample. When the main
client-bundle loads with async: true but auto-generated packs load with
defer: true (the previous default), the defer scripts execute after async
scripts, causing "Component already registered" errors or missing components.

This commit changes generated_component_packs_loading_strategy from :defer
to :async to match the main bundle loading strategy, ensuring proper
execution order for non-Redux pages.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

spec/dummy/config/initializers/react_on_rails.rb

@@ -42,5 +42,5 @@ def self.adjust_props_for_client_side_hydration(component_name, props)
   config.components_subdirectory = "startup"
   config.auto_load_bundle = true
   config.immediate_hydration = false
-  config.generated_component_packs_loading_strategy = :defer
+  config.generated_component_packs_loading_strategy = :async
 end