Add SSR warnings on useMedia/useResponsiveValue

[hectahertz]

Closes https://github.com/github/primer/issues/5283

Changelog

Introduce SSR (Server-Side Rendering) warnings to the useMedia and useResponsiveValue hooks in @primer/react, and renames useMedia to useMediaUnsafeSSR to improve clarity around SSR compatibility.

The main focus is to warn developers about potential hydration mismatches when using these hooks without a default state during SSR, and to encourage safer alternatives.

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: ed82b10

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

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Patch
@primer/styled-react	Patch

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[Copilot]

Pull Request Overview

This PR renames the useMedia hook to useMediaUnsafeSSR to better communicate the SSR safety implications of using this hook without a defaultState parameter. The rename helps developers understand that this hook can cause hydration mismatches when rendering on the server without proper configuration.

Key changes:

• Renamed useMedia to useMediaUnsafeSSR across the codebase
• Added warning documentation about SSR compatibility to both the hook and its usage in useResponsiveValue

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
packages/react/src/hooks/useResponsiveValue.ts	Updated to use useMediaUnsafeSSR and added SSR compatibility warning in documentation
packages/react/src/hooks/useMediaUnsafeSSR.tsx	Renamed hook from useMedia to useMediaUnsafeSSR and updated documentation references
packages/react/src/hooks/tests/useMedia.test.tsx	Updated test file to use renamed useMediaUnsafeSSR hook

[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!