Fix Avatar sizing in Button leadingVisual slot

[Copilot]

Fixes #7974

Avatars passed into Button's leadingVisual slot render at the wrong width. Global img { max-width: 100% } collides with the less-specific Avatar width (set via CSS var), and because Button uses min-content for the leadingVisual grid area, max-width can resolve to 0, shrinking the image.

Changelog

New

Changed

• Avatar.module.css: set min-width alongside width (base rule + all responsive breakpoints) so Avatars never shrink below their intended size.
• AvatarStack.module.css: set min-width: var(--avatar-stack-size) on .AvatarItem. The Avatar min-width resolves to each child's inline --avatarSize-regular, so without this override custom-size children rendered at their individual sizes instead of the uniform stack size.

Removed

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

Verify via the Button-with-Avatar leadingVisual case (Avatar retains its expected width) and the AvatarStack CustomSizeOnChildren story (children remain uniformly sized at the smallest child's size).

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: d60e813

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	Patch

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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.

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

[Copilot]

Pull request overview

This PR addresses a layout bug where Avatar images can collapse to an incorrect width when rendered inside Button’s leadingVisual slot (due to min-content sizing interacting with a global img { max-width: 100% } rule). The fix makes Avatars maintain their intended rendered width by enforcing a matching min-width.

Changes:

• Add min-width alongside width in the base .Avatar rule.
• Add min-width for each responsive breakpoint (narrow/regular/wide) under data-responsive.
• Add a patch changeset documenting the user-visible fix.

Show a summary per file

File	Description
packages/react/src/Avatar/Avatar.module.css	Adds min-width to prevent Avatar images collapsing under constrained grid sizing contexts.
.changeset/avatar-min-width.md	Patch changeset describing the Avatar sizing fix (notably for Button leadingVisual).

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1

[primer-integration]

Integration test results from github/github-ui PR:

  CI Failed
  VRT skipped
  Projects Passed

CI check runs linting, type checking, and unit tests. Check the workflow logs for specific failures.

VRT check ensures that when visual differences are detected, the PR cannot proceed until someone acknowledges the changes by adding the "visual difference acknowledged" label.

Need help? If you believe this failure is unrelated to your changes, please reach out to the Primer team for assistance.