Magic Link: refactor Jetpack loading indicator to use Spinner component

[Initsogar]

Fixes MARTECH-70

Proposed Changes

• Replace LoadingEllipsis with core Spinner component for a more consistent loading experience.
• Update corresponding styles to reflect the new loading spinner design.
• Enable jetpack/magic-link-signup on Live Branches environment, so this PR could be tested there. This is a legacy feature flag that was available on all environment except wpcalypso.

Before	After
CleanShot.2025-04-04.at.20.47.08.2.mp4	CleanShot.2025-04-04.at.20.46.38.mp4

Why are these changes being made?

We want to improve the Jetpack Onboarding experience.

Testing Instructions

1. Spin up a Calypso Live Branch (you will need it on step 6).
2. Spin up a Jurassic Ninja site using the latest Jetpack.
3. Go to /wp-admin/admin.php?page=my-jetpack&step=onboarding on the site.
4. Fill out your email and submit the form.
5. You should be redirected to the magic link page, where you receive the login e-mail.
6. On that page, replace the domain from wordpress.com to your Calypso Live Branch domain and navigate there.
7. Ensure the loading state uses the spinner instead of the ellipsis.

CleanShot.2025-04-04.at.22.05.16-converted.2.mp4

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-139735

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-139735&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-139735&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~19 bytes added 📈 [gzipped])

Details

name         parsed_size           gzip_size
entry-login        +76 B  (+0.0%)      +19 B  (+0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug update/jetpack-onboarding-loading-spinner on your sandbox.

[Initsogar]

This feature flag enables the magic link signup, and it was already enabled on all environments (production, stage, development, horizon), except wpcalypso, which is the one on Calypso Live Branches.

[grzegorz-cp]

👍