Fix duplicate rake task execution when Engine rake_tasks called twice

Prevents duplicate task definitions when Rails Engine's rake_tasks block
is invoked multiple times during initialization. Each rake file now uses
a guard constant to ensure tasks are only defined once.

This fixes the issue where react_on_rails:assets:webpack would run the
build command twice, causing unnecessary build time and potential issues.

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

lib/tasks/assets.rake

@@ -1,5 +1,11 @@
 # frozen_string_literal: true
 
+# Guard against loading this file multiple times
+# This can happen if Engine's rake_tasks block is called more than once during Rails initialization
+return if defined?(REACT_ON_RAILS_ASSETS_RAKE_LOADED)
+
+REACT_ON_RAILS_ASSETS_RAKE_LOADED = true
+
 # rubocop:disable Metrics/BlockLength
 namespace :react_on_rails do
   namespace :assets do

lib/tasks/generate_packs.rake

@@ -1,5 +1,11 @@
 # frozen_string_literal: true
 
+# Guard against loading this file multiple times
+# This can happen if Engine's rake_tasks block is called more than once during Rails initialization
+return if defined?(REACT_ON_RAILS_GENERATE_PACKS_RAKE_LOADED)
+
+REACT_ON_RAILS_GENERATE_PACKS_RAKE_LOADED = true
+
 # rubocop:disable Metrics/BlockLength
 namespace :react_on_rails do
   desc <<~DESC

lib/tasks/locale.rake

@@ -1,5 +1,11 @@
 # frozen_string_literal: true
 
+# Guard against loading this file multiple times
+# This can happen if Engine's rake_tasks block is called more than once during Rails initialization
+return if defined?(REACT_ON_RAILS_LOCALE_RAKE_LOADED)
+
+REACT_ON_RAILS_LOCALE_RAKE_LOADED = true
+
 require "react_on_rails/locales/base"
 require "react_on_rails/locales/to_js"
 require "react_on_rails/locales/to_json"