Addon Test: Support Storybook environment variables in Vitest

[ghengeveld]

Closes #29779

What I did

Loads environment variables configured in Storybook's main config and adds them to the Vitest env config. Sets Vite's envPrevix to include STORYBOOK_ prefixed environment variables.

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

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

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.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • 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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generateSize	77.7 MB	77.7 MB	0 B	0.82	0%
initSize	130 MB	130 MB	68 B	0.21	0%
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buildSize	6.75 MB	6.75 MB	0 B	-1.73	0%
buildSbAddonsSize	1.51 MB	1.51 MB	0 B	-	0%
buildSbCommonSize	195 kB	195 kB	0 B	-	0%
buildSbManagerSize	1.86 MB	1.86 MB	0 B	-0.41	0%
buildSbPreviewSize	0 B	0 B	0 B	-1.73	-
buildStaticSize	0 B	0 B	0 B	-	-
buildPrebuildSize	3.56 MB	3.56 MB	0 B	-1.73	0%
buildPreviewSize	3.19 MB	3.19 MB	0 B	1.73	0%
testBuildSize	0 B	0 B	0 B	-	-
testBuildSbAddonsSize	0 B	0 B	0 B	-	-
testBuildSbCommonSize	0 B	0 B	0 B	-	-
testBuildSbManagerSize	0 B	0 B	0 B	-	-
testBuildSbPreviewSize	0 B	0 B	0 B	-	-
testBuildStaticSize	0 B	0 B	0 B	-	-
testBuildPrebuildSize	0 B	0 B	0 B	-	-
testBuildPreviewSize	0 B	0 B	0 B	-	-

name	before	after	diff	z	%
createTime	24.6s	7.2s	-17s -412ms	-1.08	-240.3%
generateTime	18.8s	19.8s	1s	-0.69	5.2%
initTime	12s	12.9s	906ms	-0.56	7%
buildTime	9.9s	8.1s	-1s -797ms	-1.1	-22.1%
testBuildTime	0ms	0ms	0ms	-	-
devPreviewResponsive	4.4s	5s	606ms	-0.09	11.9%
devManagerResponsive	3.2s	3.6s	448ms	-0.05	12.1%
devManagerHeaderVisible	531ms	589ms	58ms	-0.13	9.8%
devManagerIndexVisible	580ms	622ms	42ms	-0.46	6.8%
devStoryVisibleUncached	1.8s	1.1s	-662ms	-2.98	🔰-57.7%
devStoryVisible	559ms	624ms	65ms	-0.37	10.4%
devAutodocsVisible	508ms	547ms	39ms	0.11	7.1%
devMDXVisible	462ms	542ms	80ms	0.06	14.8%
buildManagerHeaderVisible	501ms	803ms	302ms	1.54	🔺37.6%
buildManagerIndexVisible	577ms	902ms	325ms	1.79	🔺36%
buildStoryVisible	466ms	731ms	265ms	1.19	36.3%
buildAutodocsVisible	390ms	628ms	238ms	1.52	🔺37.9%
buildMDXVisible	394ms	512ms	118ms	0.4	23%

Greptile Summary

Based on the provided information, I'll create a concise summary of the pull request changes:

Adds support for Storybook environment variables in the Vitest plugin, enabling proper handling of both Storybook-configured and Vite environment variables during testing.

• Added environment variable loading from Storybook's main config via presets.apply('env') in code/addons/test/src/vitest-plugin/index.ts
• Added STORYBOOK_ to Vite's envPrefix array to support Storybook-prefixed variables
• Added env extension to Presets interface in code/core/src/types/modules/core-common.ts
• Maintains proper precedence by merging Storybook env variables with Vitest config
• Handles edge cases with nullish coalescing for undefined config objects

[greptile-apps]

LGTM

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