[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'

[cirdes]

it re-implements Stimulus target lookup by hand and hard-codes the controller identifier inside a selector string. If the controller is ever renamed, the input target moves, or the input gets wrapped in another element, this silently stops working, and the controller is now coupled to another instance's internal markup.

Using querySelector is a code smell in hotwire