ActionList: Support mixed descriptions

[obvioussean]

Refs github/github-ui#22256

Adds first-class ActionList support for rendering one inline description beside an item label and one block description beneath the same label. This gives consumers a supported way to add a second detail line, such as estimated cost, without hand-rolling label and description styling inside ActionList.Item children.

Changelog

New

• ActionList.Item supports rendering one inline ActionList.Description and one block ActionList.Description together.

Changed

• Added docs metadata and a Storybook feature story for the mixed-description layout.

Removed

• None.

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Validated the new mixed-description path with:

• npm run build
• npm run type-check
• npm run lint
• npm run lint:css
• npm run format:diff
• npm test -- packages/react/src/ActionList/ActionList.test.tsx
• Storybook visual check in Chromium for components-actionlist-features--inline-and-block-description

I also ran the full npm test; it failed on an unrelated local AnchoredOverlay click timeout after the ActionList suite passed.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github-ui (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 89b6c1b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

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[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

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