[Bug Fix] Prevent Command dialog stacking

[djalmaaraujo]

Summary

• Mark cloned Command dialog content so the controller can detect an already-open dialog
• Refocus the existing dialog input instead of appending another modal on repeated keybindings
• Update docs controller copy and add component markup coverage

Closes #230

Testing

• docker run --rm -v ruby_ui_bundle:/usr/local/bundle -v /Users/djalmaaraujo/dev/linkana/ruby_ui-issue-230:/workspace -w /workspace/gem ruby:3.4.7 bash -lc 'bundle install && bundle exec rake test TEST=test/ruby_ui/command_test.rb'