UI: Fix test provider event handling on startup

[ghengeveld]

What I did

Replaced useEffect with useLayoutEffect in order to have event listeners registered before rendering the test providers' UI. This is necessary because the VTA emits a progress report event when it has a warning (e.g. when not logged in to Chromatic), which happens on first render of its Description. The event is used to set runnable: false on the VTA, and if we miss this event, the VTA will have a Run button and respond to "Run all", which results in the addon getting stuck in "pending" state.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

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Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
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  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

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buildSbPreviewSize	0 B	0 B	0 B	-	-
buildStaticSize	0 B	0 B	0 B	-	-
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buildPreviewSize	3.3 MB	3.3 MB	0 B	-0.07	0%
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testBuildSbManagerSize	0 B	0 B	0 B	-	-
testBuildSbPreviewSize	0 B	0 B	0 B	-	-
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testBuildPreviewSize	0 B	0 B	0 B	-	-

name	before	after	diff	z	%
createTime	6.7s	9s	2.3s	-0.6	25.9%
generateTime	19.2s	20.5s	1.3s	0.26	6.4%
initTime	12.8s	14s	1.2s	-0.1	8.9%
buildTime	12.8s	10s	-2s -755ms	0.02	-27.4%
testBuildTime	0ms	0ms	0ms	-	-
devPreviewResponsive	5.5s	4.7s	-803ms	-0.5	-16.8%
devManagerResponsive	4s	3.5s	-432ms	-0.48	-12%
devManagerHeaderVisible	651ms	636ms	-15ms	0.55	-2.4%
devManagerIndexVisible	723ms	664ms	-59ms	0.42	-8.9%
devStoryVisibleUncached	1.7s	1.8s	132ms	0.36	7.2%
devStoryVisible	720ms	663ms	-57ms	0.37	-8.6%
devAutodocsVisible	578ms	524ms	-54ms	-0.08	-10.3%
devMDXVisible	676ms	529ms	-147ms	-0.08	-27.8%
buildManagerHeaderVisible	694ms	567ms	-127ms	-0.56	-22.4%
buildManagerIndexVisible	780ms	648ms	-132ms	-0.65	-20.4%
buildStoryVisible	652ms	525ms	-127ms	-0.58	-24.2%
buildAutodocsVisible	551ms	413ms	-138ms	-0.79	-33.4%
buildMDXVisible	586ms	455ms	-131ms	-0.13	-28.8%

Greptile Summary

This PR changes the event listener registration timing in SidebarBottom from useEffect to useLayoutEffect to prevent the Visual Testing Addon (VTA) from missing critical initial render events.

• Changed useEffect to useLayoutEffect in code/core/src/manager/components/sidebar/SidebarBottom.tsx to register event listeners before UI rendering
• Updated @chromatic-com/storybook dependency from 3.2.0 to 3.2.2 in code/package.json
• Fixes VTA getting stuck in 'pending' state when warnings occur during initial render (e.g., when not logged into Chromatic)

[greptile-apps]

LGTM

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