feat: implement style api for tabs component

[mxschll]

Description

Extends the tabs component with a style API for customization, allowing developers to override default component styles.

Related links, issue #, if available: n/a

How has this been tested?

• Added unit tests for style prop validation and CSS class application
• Screenshot tests passed without visual regressions

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.00%. Comparing base (abb494e) to head (b4b9e62).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4027   +/-   ##
=======================================
  Coverage   96.99%   97.00%           
=======================================
  Files         861      863    +2     
  Lines       25207    25268   +61     
  Branches     9098     9141   +43     
=======================================
+ Hits        24450    24511   +61     
- Misses        710      751   +41     
+ Partials       47        6   -41     

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[mxschll]

Removing transparent because it overrides custom styles for invalid or disabled. Removal caused no visual regressions. Keeping this property would prevent custom styles from taking effect.

[gethinwebster]

I think focusRing color might need states, because it is displayed over the background color. So, for example, it might not be possible to find an accessible focus ring color that works over both default and active background colors

[mxschll]

I propose we add this to the existing components as well (e.g. button).

[gethinwebster]

For most components it appears outside the component itself so it's less of an issue as the "background" its displayed against isn't state-dependent. I guess the other alternative is to explore whether the ring could be moved outside the background here?

[mxschll]

Right, it's also displayed outside of the regular button component. That would make the API more streamlined across components, but I'm not sure if moving the ring will break something... I'll try to explore this further.

[gethinwebster]

I don't think the naming here is clear, I would suggest tabButton

[gethinwebster]

I think this should be part of the tabButton

[gethinwebster]

the structure/naming here isn't clear: what's the difference between divider and headerDivider?