Change primitives.css to use imports and add viewport.css

[lukasoppermann]

Summary

Change primitives.css to use imports and add viewport.css

This is one step in https://github.com/github/primer/issues/4506

@langermank is there any reason you removed viewports from primer.css? It is added in dotcom in the index.scss

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[changeset-bot]

🦋 Changeset detected

Latest commit: 643dbe1

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

This PR includes changesets to release 1 package

Name	Type
@primer/primitives	Minor

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[Copilot]

Pull Request Overview

This PR refactors the CSS build system to use imports in primitives.css and re-enables viewport.css. The change simplifies CSS loading by consolidating multiple imports into a single primitives.css file and restores viewport styles that were previously excluded.

• Modified build script to generate import statements instead of concatenating CSS content
• Re-enabled viewport.css by commenting out its exclusion filter
• Updated Storybook preview to use the consolidated primitives.css import

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
scripts/buildTokens.ts	Modified to generate CSS imports and re-enable viewport.css in the build
docs/storybook/.storybook/preview.css	Simplified to use single primitives.css import instead of multiple individual imports

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