admin-ui: Update package README to clarify purpose and distinguish from ui package

[aduth]

What?

Updates @wordpress/admin-ui package README description to clarify the purpose of the package and distinguish it from other component packages like @wordpress/ui and @wordpress/components.

Why?

To make it clearer what types of code would be expected to belong in this package.

Before these changes, related packages had very similar descriptions which made it difficult for someone to differentiate:

• @wordpress/ui: "React UI components for the WordPress Design System, built on themeable design tokens"
• @wordpress/components: "generic WordPress components to be used for creating common UI elements shared between screens and features of the WordPress dashboard"
• @wordpress/admin-ui: "Generic components to be used to build the Admin UI"

This creates difficulty for both maintainers and consumers:

• Maintainers may struggle to know which component belongs in which package
• Consumers may not understand where to expect to find components they need

How?

This has evolved from a few recent discussions about the purpose of the @wordpress/admin-ui package and fit for certain components, as well as current Page component and enhancements supporting page header standardization.

Starting from a fundamental question: Why does this package exist? Personally, my view is that it holds value both in how we abstract components, and in what it contains today, which is largely the composition of common admin page layouts. It's a higher level of abstraction than what we expect to exist in @wordpress/ui, similar to how @wordpress/dataviews composes design system components for a functional purpose. This is all in service of the goal to provide a cohesive, predictable experience for users.

Testing Instructions

This is documentation-only changes. Review the changes for accuracy.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: aduth <aduth@git.wordpress.org>
Co-authored-by: youknowriad <youknowriad@git.wordpress.org>
Co-authored-by: ciampo <mciampini@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[youknowriad]

Thanks, that's a way better description haha

[github-actions]

Flaky tests detected in 7283c34.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/23817591743
📝 Reported issues:

• [Flaky Test] post title and content are editable and blocks can be inserted #76524 in /test/e2e/specs/editor/various/post-content-focus-mode.spec.js
• [Flaky Test] should show correct homepage actions based on current homepage or posts page #68892 in /test/e2e/specs/site-editor/homepage-settings.spec.js

[ciampo]

👏