feat: add configurable responsive columns to Board

[mahayash315]

Description

Adds an optional, backward-compatible columnLayout prop to Board. Consumers can configure column counts at Cloudscape container breakpoints such as xs, s, m, and l.

Unspecified breakpoints inherit the nearest narrower configured value. Existing Board behavior remains unchanged when the prop is omitted.

Related links, issue #, if available: cloudscape-design/components#3256

How has this been tested?

• npm run build
• npm run lint
• npm run test:unit — 375 tests pass
• Manually verified responsive layouts and keyboard movement on the new development page

The functional test stage was not run locally because ChromeDriver is unavailable.

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?

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.