[A11y] Pricing options markup order

[danielguillan]

Summary

Resolves https://github.com/github/primer/issues/3727 and https://github.com/github/primer/issues/3729

Makes the content order in PricingOptions accessible by ensuring the heading is always first in the markup. Visual element order remains unchanged.

List of notable changes:

• PricingOptions children are now rendered in a structured, predictable order.
• Removed primary accent color override from stories to restore accessible contrast from the default accent color.

What should reviewers focus on?

• Any visual regressions?
• Test responsive behavior

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

[changeset-bot]

🦋 Changeset detected

Latest commit: e9c4e25

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]

Looks good, thanks @danielguillan 🙌

What do you think about adding a unit test for this (as a follow up) given how important element ordering is? It's come up a few times now, and is something we'd likely want to not regress on during future refactors.