Add deprecation warning for :global usage

[Mad-Kat]

Deprecates :global() selectors to align webpack projects with Turbopack and upcoming Vite integrations, which already require native CSS transpilation.

Changes:

• Build-time warning when :global() is detected
• New ESLint rule yak/css-global-deprecated
• Migration docs at /docs/migration-to-native-css
• suppressDeprecationWarnings option for gradual migration

To migrate: experiments: { transpilationMode: 'Css' } in next.config.js and remove :global() from your selectors

[changeset-bot]

🦋 Changeset detected

Latest commit: d5677c6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

Name	Type
next-yak	Minor
yak-swc	Minor
eslint-plugin-yak	Minor
next-yak-example	Patch
vite-yak-example	Patch
benchmarks	Patch
docs	Patch

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[codspeed-hq]

CodSpeed Performance Report

Merging #448 will not alter performance

_{Comparing feat/add-global-deprecation-warning (d5677c6) with main (846cc4c)}

Summary

✅ 12 untouched
⏩ 12 skipped¹

Footnotes

1. 12 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩