docs(storybook): restore story defaults dropped by the Storybook 9 upgrade

[frankieyan]

Short description

Box's Margin Story crashes because it expected a margin arg to be provided, but it was never supplied. This is because it was passed in through argTypes.margin.defaultValue, and Storybook dropped defaultValue as a source of initial args in v7, in favour of args.

On top of fixing the crash, we also remove all other defaultValues, and move them into args instead.

Reference

• feat: upgrade storybook 6.5 -> 9 + vite #1038
• Storybook ArgTypes API

Demo

Margin Story crashed on mount. The empty margin control in the "before" screenshot is the root cause:

Before	After

Interactive Props Story didn't crash, but rendered an empty canvas with every control unset:

Before	After

Padding Story rendered, but with padding undefined:

Before	After

Test plan

• Start Storybook locally and navigate to http://localhost:6006/?path=/story/%F0%9F%93%90-layout-box--margin-story
  • The story doesn't crash, and seven bordered boxes render

PR Checklist

• Added tests for bugs / new features
• Updated docs (storybooks, readme)
• Reviewed and approved Chromatic visual regression tests in CI

[doistbot]

This PR fixes a Storybook 9 crash by migrating all argTypes.defaultValue entries into args blocks, and simplifies the storybook helper functions by dropping their defaultValue parameter.

Few things worth tightening:

• A few stories still rely on selectWithNone()/selectSize() without matching args (e.g., Columns/AlignmentStory, Stack/InteractivePropsStory, heading/text playgrounds). They'll still open with blank controls in Storybook 9 — either keep the helper default or add explicit args: { …: 'none' } at each remaining site.
• space: 'medium' is now repeated across four story-level args blocks in columns.stories.tsx. Hoisting it to export default.args would give a single source of truth and make future stories easier to get right.

I also included a few optional follow-up notes in the details below.

Optional follow-up notes (2)

• src/utils/storybook-helper.tsx:24: Removing the implicit 'none' default here leaves a few stories regressed, because they still inherit selectWithNone()/selectSize() argTypes without defining matching args. For example, Columns/AlignmentStory (space, align, alignY), Stack/InteractivePropsStory (space, align, dividers), and the heading/text playgrounds (size, lineClamp, align) will still load with empty controls in Storybook 9. Either keep the helper default until each caller has explicit args, or add args: { ...: 'none' } at the remaining story/meta sites.
• src/columns/columns.stories.tsx:287: space: 'medium' is now repeated in four story-level args blocks in this file. Since space is already a file-level control and AlignmentStory uses the same prop, hoisting this to export default.args would give the file one source of truth for the initial spacing and make future story additions less easy to miss.

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