refs TryGhost/Team#3122
- Fixed that preview takes data from user input before saving on
backend.
---
<!-- Leave the line below if you'd like GitHub Copilot to generate a
summary from your commit -->
<!--
copilot:summary
-->
### <samp>🤖 Generated by Copilot at 54d5b2d</samp>
This pull request adds the ability to preview the announcement bar in
the Ghost admin panel and the theme settings. It also adds a
confirmation dialog to discard or save unsaved changes before leaving
the announcement bar settings. It refactors some components and methods
to remove unnecessary or redundant calls to save the settings. It
modifies the `ghost_head` helper, the `theme-management` service, and
the `announcement-bar/src` files to support the preview feature.
refs TryGhost/Team#3052
<!-- Leave the line below if you'd like GitHub Copilot to generate a
summary from your commit -->
<!--
copilot:summary
-->
### <samp>🤖 Generated by Copilot at 7173288</samp>
This pull request adds new components and settings for the announcement
bar feature, which allows the user to customize the content, background,
and visibility of a banner that appears on the site.
