Fix doctor rake task LoadError with excluded task_helpers

The doctor.rake task was trying to require "../../rakelib/task_helpers"
but the rakelib directory is excluded from gem packaging in the gemspec.
This caused LoadError when using the packaged gem.

Changes:
- Remove require_relative "../../rakelib/task_helpers" from doctor.rake
- Remove include ReactOnRails::TaskHelpers (unused in the task)
- Add test to ensure rake file loads without missing dependencies

The doctor task functionality is preserved and works correctly without
the excluded TaskHelpers module.

Fixes the issue introduced in commit 27dba50 where doctor.rake was added
with a reference to the excluded rakelib directory.

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

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

Author: justin808

lib/tasks/doctor.rake

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-require_relative "../../rakelib/task_helpers"
 require_relative "../react_on_rails"
 require_relative "../react_on_rails/doctor"
 
@@ -38,7 +37,6 @@ rescue LoadError
 end
 
 namespace :react_on_rails do
-  include ReactOnRails::TaskHelpers
 
   desc "Diagnose React on Rails setup and configuration"
   task :doctor do

spec/lib/react_on_rails/doctor_rake_task_spec.rb

@@ -16,6 +16,12 @@
       expect(Rake::Task.task_defined?("react_on_rails:doctor")).to be true
     end
 
+    it "can be loaded without requiring missing task_helpers" do
+      # This test ensures the rake file doesn't try to require excluded files
+      # that would cause LoadError in packaged gems
+      expect { load rake_file }.not_to raise_error
+    end
+
     it "can be invoked without errors" do
       # Mock the Doctor class to avoid actual diagnosis
       doctor_instance = instance_double(ReactOnRails::Doctor)