Breadcrumbs: Only show the previous breadcrumb on narrow viewports

[liuliu-dev]

Closes https://github.com/github/primer/issues/6371

Changelog

New

On narrow viewports (≤544px), breadcrumbs collapse to show only the previous (parent) item as a back link. The current page is hidden since you're already on it. Consumers can pass narrowVisibleItems to control how many items stay visible.

Rollout strategy

• Minor release

Testing & Reviewing

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: fb2e5e1

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[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.

To publish a canary release for integration testing, apply the Canary Release label to this PR.

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/18167

[primer-integration]

Integration test results from github/github-ui:

  CI Waiting
  VRT Passed
  Projects Passed