Support a multi-action Card variant with ButtonGroup #1460

Summary

Add a supported card-like composition that can render a native ButtonGroup with one or two independent actions, similar to the action patterns available in Hero and CTABanner.

Our preferred outcome is a Card variant designed for multiple actions. If that does not fit Card’s interaction model, an acceptable alternative would be a Pillar variant with Pillar.ButtonGroup support and a visual treatment that looks more like a Card than the current borderless Pillar presentation.

Context

We are exploring new sections for a marketing page that need card-like content with multiple calls to action. Today:

• Card provides the desired visual treatment, but requires a single href and uses a stretched heading link so the entire card represents one destination.
• Pillar supports more flexible content composition, but filters out ButtonGroup and does not provide the Card-like presentation needed for this use case.
• Hero and CTABanner already expose native compound ButtonGroup components.

Desired composition

The exact API and variant name are open, but the intended content model is:

<Card variant="multi-action">
  <Card.Heading>Build with confidence</Card.Heading>
  <Card.Description>Supporting copy for the section.</Card.Description>
  <Card.ButtonGroup>
    <Button as="a" href="/get-started">Get started</Button>
    <Button as="a" href="/learn-more">Learn more</Button>
  </Card.ButtonGroup>
</Card>

The actions must remain independent and directly interactive; the existing stretched Card link must not overlap or compete with them.

Alternative direction

If multiple independent actions should remain outside Card’s single-destination model, extend Pillar instead:

• Add Pillar.ButtonGroup, delegating to the shared ButtonGroup.
• Add a Card-like Pillar presentation with appropriate surface, spacing, background, and optional border treatment.
• Support both start- and center-aligned content.

Acceptance criteria

• Provide a supported card-like component composition with one or two native ButtonGroup actions.
• Preserve valid, accessible interaction semantics without overlapping links or click targets.
• Reuse the shared ButtonGroup API and behavior.
• Support responsive layouts and start/center alignment where applicable.
• Preserve existing Card and Pillar behavior by default.
• Add unit, Storybook, visual, and documentation coverage.