chore(deps): update to vite 8 and latest related vite plugins

[joshblack]

Update our project locally to use Vite 8 🎉 This includes the rolldown-powered version of Vite.

Changelog

New

Changed

• Update codesandbox to use latest vite deps
• Update react to use latest vite deps
• Update styled-react to use latest vite deps
• Update test config for styled-react so that it can resolve exports with JSX

Removed

Rollout strategy

• None; if selected, include a brief description as to why

This is an internal change to test dependencies

[changeset-bot]

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Latest commit: 60a4da7

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[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

To publish a canary release for integration testing, apply the Canary Release label to this PR.

[Copilot]

Pull request overview

This PR updates the repo’s Vite toolchain to Vite 8 (rolldown-powered) and aligns related Vite React plugin usage/versions across workspaces, including ensuring @primer/styled-react’s Vitest setup can correctly handle JSX-based exports.

Changes:

• Bump vite to ^8.0.16 at the repo root and update lockfile accordingly.
• Bump @vitejs/plugin-react to ^6.0.2 in @primer/react and @primer/styled-react (and in the CodeSandbox example).
• Add @vitejs/plugin-react to packages/styled-react/vitest.config.ts to enable JSX-aware transforms in the node test config.

Show a summary per file

File	Description
packages/styled-react/vitest.config.ts	Adds Vite React plugin to Vitest node config to support JSX transforms.
packages/styled-react/package.json	Updates @vitejs/plugin-react devDependency to v6.
packages/react/package.json	Updates @vitejs/plugin-react devDependency to v6.
package.json	Adds vite@^8.0.16 to root devDependencies.
package-lock.json	Lockfile updates for Vite 8 / plugin-react 6 and their new transitive deps (rolldown/lightningcss/etc).
examples/codesandbox/package.json	Updates CodeSandbox example’s Vite/tooling deps to Vite 8 + plugin-react 6.

Copilot's findings

• Files reviewed: 5/6 changed files
• Comments generated: 1