feat(Table): Add whitespace below Caption

[VincentSmedinga]

Describe the pull request

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What

1. Applies a margin below a Table Caption.
2. Adds instructions for making a Table Caption with both a Heading and additional content accessible.

Why

1. There isn’t enough whitespace between the caption and the body of the table.
2. While working on the spacing, I came across a best practice for the markup of a table caption with both a heading and a description, so I decided to document it. Moving this into a separate PR seems unnecessary – it’s in the Storybook package which doesn’t publish a changelog.

How

n/a

Checklist

Before submitting your pull request, please ensure you have done the following. Check each checkmark if you have done so or if it wasn't necessary:

• Add or update unit tests
• Add or update documentation
• Add or update stories
• Add or update exports in index.* files
• Comment /chromatic test and verify visual regression tests pass
• Start the PR title with a Conventional Commit prefix, as explained here.

Additional notes

• At first, I also implemented an option to place the Caption below the Table. But that does’t seem to be so useful after all, so I’ve removed it again.
• Then I added some documentation and an example of what I learned.

[Copilot]

Pull request overview

This PR adds support for rendering a table caption visually below the table via a new side="bottom" prop on TableCaption, with accompanying styling and design token support, and adjusts TypeScript typing to preserve compound-component subcomponent prop types.

Changes:

• Add side?: 'bottom' to TableCaption and apply a ams-table__caption--bottom modifier class when set.
• Update table caption styling to support bottom positioning and add configurable margins via CSS variables.
• Strengthen TypeScript types for forwardRef usage and the Table compound component to preserve subcomponent prop types.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/react/src/Table/TableCaption.tsx	Adds side="bottom" prop and modifier class; uses explicit generics on forwardRef for better prop preservation.
packages/react/src/Table/Table.tsx	Adds explicit compound-component typing to preserve subcomponent prop types through Object.assign.
packages/css/src/components/table/table.scss	Adds bottom-caption styling (caption-side: bottom) and margin handling for top vs bottom captions.
packages-proprietary/tokens/src/components/ams/table.tokens.json	Introduces caption margin design tokens used by the updated SCSS variables.

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[RubenSibon]

This PR's title and description does not seem to match the changes it makes. It also adds a Story. Can you adjust?

[RubenSibon]

/chromatic test

The old one is outdated.

[RubenSibon]

/chromatic test

The old one is outdated.

@Evi-2003, with the change to kick of the builds manually we do have to be alert if an existing build is out-of-date. It does add some cognitive load. It's absolutely not a major inconvenience, but still good to be aware of.

[RubenSibon]

Adjust the test Story for Chromatic.

[VincentSmedinga]

This PR's title and description does not seem to match the changes it makes. It also adds a Story. Can you adjust?

@RubenSibon Sure, I’ve updated the PR description. We don’t usually mention documentation changes in the changelog, so I’ve left the title alone.

I’ve added a Paragraph into the Table Caption of the test story as well, so Chromatic tests both the whitespace below the caption and the accessible name of the table.

[VincentSmedinga]

/Chromatic test