docs: show how to send events between components in the same UI

[totally-not-ai]

Review risk: two-way door — adds one section and three example classes to the component events reference page; nothing existing changes.

Summary

Adds a Communicating Between Components in the Same UI section to articles/flow/component-internals/events.adoc. It shows how to use the UI's event bus to send events between components that don't have references to each other. The example is a search field in the main layout that tells the current view to filter its content.

The docs so far only showed an event bus stored in the session. Firing events on the UI with ComponentUtil.fireEvent() / ComponentUtil.addListener() wasn't documented anywhere.

What changed

• New section after "Firing Events from the Server". It covers:
  • Firing a ComponentEvent on the UI with ComponentUtil.fireEvent().
  • Listening with ComponentUtil.addListener() inside whenAttached(), so the listener is removed on detach and the UI doesn't keep a reference to a detached view.
  • When to use something else: an event bus in the VaadinSession to reach all of the user's tabs, or a local signal when the components share state rather than react to events.
• New compiled examples SearchEvent, GlobalSearchField and OrdersView in com.vaadin.demo.reference.componentinternals.events.ui.

This replaces the "Communicate between components attached to one UI" recipe from the retired Vaadin Cookbook.

Test summary

• The new example classes compile with the rest of the docs sources (mvn compile).

🤖 Generated with Claude Code

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URL: https://docs-preview-pr-6256.fly.dev

Changed pages

Added content is highlighted in green; removed content is marked in red on each page.

• flow/component-internals/events — modified, +29/-0 lines

Other changed files

• src/main/java/com/vaadin/demo/reference/componentinternals/events/ui/SearchEvent.java (added)

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