feat(ui): update uxdocs Messages and Notifications

[franzheidl]

Summary

Update the uxdocs so Toast and NotificationManager are reflected/included.

Related Issues

Closes #1825

Checklist

• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have made corresponding changes to the documentation (if applicable).
• My changes generate no new warnings or errors.
• I have created a changeset for my changes.

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Latest commit: 0986473

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[Copilot]

Pull request overview

Updates Juno UX documentation to reflect that Toast-based notifications are now available via NotificationManager and the toast() API, replacing outdated guidance that notifications are not implemented.

Changes:

• Replaces the “not yet available” notice with updated Notifications usage guidance.
• Documents NotificationManager vs Toast, including lifecycle responsibilities and recommended usage patterns.
• Adds guidance around dismissibility, queuing, and auto-dismiss behavior.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.