Improve the layout responsiveness of SubdomainNavBar

[danielguillan]

Summary

This pull request improves the layout responsiveness of SubdomainNavBar. Fixes #581.

🔗 Storybook

List of notable changes:

• Uses the small button variant for CTAs.
• Makes the title text responsive by relying on the Text component instead of fixed CSS values.
• Adjusts gap in the title area at different viewport sizes.
• Adapts link paddings at different viewport sizes.

What should reviewers focus on?

• Test the changes in Storybook at different viewport sizes

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
• New visual snapshots have been generated / updated for any UI changes
• 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:

Before	After

[changeset-bot]

🦋 Changeset detected

Latest commit: c91771b

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

This PR includes changesets to release 6 packages

Name	Type
@primer/react-brand	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

[github-actions]

🟢 No visual differences found

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

[rezrah]

This is great, thanks @danielguillan 🙌

FYI, the VRT test is failing for one of the stories you mentioned. Let me know if you'd like a hand fixing it.

[simmonsjenna]

Looks good! 👍