Add prerelease flags to reconstruct_command and test coverage

- Store shakapacker_prerelease and react_on_rails_prerelease as instance variables
- Include --shakapacker-prerelease and --react-on-rails-prerelease in reconstructed command
- Add test coverage for prerelease flags in reconstruct_command

This ensures demos created with prerelease flags can be accurately recreated
from the metadata file's command field.

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

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

Author: justin808

lib/demo_scripts/demo_creator.rb

@@ -28,6 +28,8 @@ def initialize(
       @scratch = scratch
       @skip_playwright = skip_playwright
       @typescript = typescript
+      @shakapacker_prerelease = shakapacker_prerelease
+      @react_on_rails_prerelease = react_on_rails_prerelease
       demos_base_dir = scratch ? 'demos-scratch' : 'demos'
       @demo_dir = File.join(demos_base_dir, demo_name)
       @config = Config.new(
@@ -505,6 +507,8 @@ def reconstruct_command
       cmd_parts << '--scratch' if @scratch
       cmd_parts << '--typescript' if @typescript
       cmd_parts << '--skip-playwright' if @skip_playwright
+      cmd_parts << '--shakapacker-prerelease' if @shakapacker_prerelease
+      cmd_parts << '--react-on-rails-prerelease' if @react_on_rails_prerelease
       if @config.shakapacker_version != Config::DEFAULT_SHAKAPACKER_VERSION
         cmd_parts << "--shakapacker-version=\"#{@config.shakapacker_version}\""
       end

spec/demo_scripts/demo_creator_spec.rb

@@ -743,5 +743,19 @@
       expect(command).to include('--rails-args="--skip-test,--api"')
       expect(command).to include('--react-on-rails-args="--redux,--typescript"')
     end
+
+    it 'includes prerelease flags when enabled' do
+      creator = described_class.new(
+        demo_name: demo_name,
+        shakapacker_prerelease: true,
+        react_on_rails_prerelease: true,
+        dry_run: true,
+        skip_pre_flight: true
+      )
+
+      command = creator.send(:reconstruct_command)
+      expect(command).to include('--shakapacker-prerelease')
+      expect(command).to include('--react-on-rails-prerelease')
+    end
   end
 end