feat(OnyxTabs): support horizontal scrolling when overflowing

[larsrickert]

Relates to #2079

• support horizontal scrolling when not all tabs fit into the available width
• add property size to change the font style
• add CSS variable --onyx-outline-width and use it in all components for consistency
• make Storybook examples more realistic
• fix vertical alignment of tab text if its not selected

Checklist

• The added / edited code has been documented with JSDoc
• If a new component is added, at least one Playwright screenshot test is added
• A changeset is added with npx changeset add if your changes should be released as npm package (because they affect the library usage)

[changeset-bot]

🦋 Changeset detected

Latest commit: e6b00fd

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

This PR includes changesets to release 6 packages

Name	Type
sit-onyx	Minor
demo-app	Patch
playground	Patch
@sit-onyx/chartjs-plugin	Major
@sit-onyx/nuxt	Major
@sit-onyx/vitepress-theme	Major

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