Fix hydration mismatch in markup in useReducedMotion hook

[rezrah]

Summary

Fixes a hydration mismatch in components that use the useReducedMotion hook.

Before: initial mount value can be different between client and server
After: initial mount value is the same (false) and set correctly in the client in subsequent render (SSR-safe)

This makes the components SSR-safe, but could also lead to flash of animation issues but we can mitigate that in CSS.

List of notable changes:

• Change initial state value for useReducedMotion to false instead of setting it through the initializer function

What should reviewers focus on?

Steps to test:

Supporting resources (related issues, external links, etc):

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• UI Changes contain new visual snapshots (generated by adding update snapshots label to the PR)
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

Screenshots:

Please try to provide before and after screenshots or videos

Before	After

[changeset-bot]

🦋 Changeset detected

Latest commit: c34e63c

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

This PR includes changesets to release 8 packages

Name	Type
@primer/react-brand	Patch
@primer/brand-docs	Patch
@primer/brand-css	Patch
@primer/brand-primitives	Patch
@primer/brand-e2e	Patch
@primer/brand-fonts	Patch
@primer/brand-config	Patch
@primer/brand-storybook	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

🟢 No design token changes found

[Copilot]

Pull request overview

This PR fixes a hydration mismatch issue in the useReducedMotion hook by changing the initial state from a lazy initializer that checks window.matchMedia to a simple false value. The fix ensures consistent rendering between server and client on initial mount, with the correct value being set in a useEffect after hydration.

Changes:

• Modified useReducedMotion hook to initialize with false instead of checking media query during initialization
• Added changeset documenting the SSR hydration fix for Hero, LogoSuite, and TextCursorAnimation components

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/react/src/hooks/useReducedMotion.ts	Changed useState initialization from lazy initializer checking window.matchMedia to simple false value
.changeset/fuzzy-spiders-chew.md	Added patch-level changeset documenting the hydration fix

[github-actions]

🟢 No unit test coverage changes found

All components and hooks with tests maintain the same coverage as the main branch.

[github-actions]

🟢 No visual differences found

Our visual comparison tests did not find any differences in the UI.

[rezrah]

Going to close this for now as this doesn't seem to be root cause for the hydration issue in dotcom