Newsletter: Move admin notices and JITMs below page header

[vianasw]

Fixes JETPACK-1484

Proposed changes

• Move GlobalNotices to render immediately after the <AdminPage> open tag, before the form content (was previously at the bottom after all sections)
• Add a #jp-admin-notices container for JITM injection, positioned below the header in its own zero-spacing Container/Col pair
• Use CSS logical properties (margin-inline-end, margin-block) for RTL-safe JITM card styling

This follows the same pattern established in #47558 for My Jetpack, Social, and Search — the Newsletter page was missed in that PR.

Other information

• Generate changelog entries for this PR (using AI).

Related product discussion/links

• Follow-up to Fix admin notices and JITMs rendering inside page headers #47558

Does this pull request change what data or activity we track or use?

No.

Testing instructions

1. Enable the Newsletter settings page feature flag by adding this to a mu-plugin:

   add_filter( 'jetpack_wp_admin_newsletter_settings_enabled', '__return_true' );

2. Navigate to Jetpack → Newsletter in wp-admin
3. Trigger a notice (e.g., save a setting) — verify it appears below the header, not inside it
4. Optionally inject a fake JITM via the jetpack_jitm_received_envelopes filter to verify JITM placement below the header

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack or WordPress.com Site Helper), and enable the fix/newsletter-admin-notices-below-header branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/newsletter-admin-notices-below-header

bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/newsletter-admin-notices-below-header

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Review, ...).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

---

Follow this PR Review Process:

1. Ensure all required checks appearing at the bottom of this PR are passing.
2. Make sure to test your changes on all platforms that it applies to. You're responsible for the quality of the code you ship.
3. You can use GitHub's Reviewers functionality to request a review.
4. When it's reviewed and merged, you will be pinged in Slack to deploy the changes to WordPress.com simple once the build is done.

If you have questions about anything, reach out in #jetpack-developers for guidance!

[jp-launch-control]

Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report · JS report

[enejb]

Works well.

I think this is an improvement from before.

Although I am not a big fan of the current max-width approach.

Should it be 100% like this

Or the same as the content like this. (660px)