feat: Use flexible layout for columns > 4 without minColumnWidth

[ekatza]

Description

This change enables ColumnLayout to automatically use flexible layout when more than 4 columns are specified without an explicit minColumnWidth prop. Previously, flexible layout was only used when minColumnWidth was set, limiting the component to 4 columns maximum in grid mode.

The change modifies the condition in src/column-layout/internal.tsx to use FlexibleColumnLayout when either minColumnWidth is provided OR columns > 4.

Related links, issue #, if available: AWSUI-61702

How has this been tested?

• Added unit test in src/column-layout/__tests__/column-layout.test.tsx verifying that 5 columns render correctly without minColumnWidth
• Added integration test in src/column-layout/__tests__/with-css.test.tsx verifying flexible layout is used with 5 columns
• Added test case to pages/column-layout/min-width.permutations.page.tsx for visual validation

To validate manually:

1. View the deployed dev pages from the CI pipeline (click "View deployment" link)
2. Navigate to /light/column-layout/min-width-permutations
3. Verify the 5-column layout renders correctly using flexible layout

Review checklist

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

Correctness

• Changes include appropriate documentation updates. - Updated JSDoc comments in interfaces.ts to remove 4-column limitation and document behavior for 5+ columns
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md. - Fully backward-compatible; only affects new use case (columns > 4 without minColumnWidth). Previous 5+ columns without minColumnWidth set was not supported.
• Changes do not include unsupported browser features, see CONTRIBUTING.md. - Uses existing FlexibleColumnLayout implementation
• Changes were manually tested for accessibility, see accessibility guidelines. - Uses existing accessible FlexibleColumnLayout component

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function. - n/a

Testing

• Changes are covered with new/existing unit tests? - New unit test added
• Changes are covered with new/existing integration tests? - n/a - component has no integration tests; unit tests should be sufficient for this change

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