fix(mui): apply Link styling props to MuiLink instead of span in Breadcrumb

[Purav-Kanda]

Resolves #7462

#7463 already proposes the same one-line fix, but adds no test coverage. The issue itself calls out that the existing breadcrumbTests suite only checks structure (text/href/icon), never styling — which is exactly why this regression shipped unnoticed. This PR includes the fix and closes that gap with a regression test that fails against the buggy <span> implementation and passes against the fix.

What's the problem?

@refinedev/mui's Breadcrumb renders links through an internal LinkRouter helper, typed to accept MUI LinkProps (sx, underline, color, variant) but spreading them onto a bare <span> instead of an MUI component — so the props do nothing and leak as invalid DOM attributes (e.g. sx="[object Object]").

Regression from the v5 migration (#6945, commit 5d63ada), which rewrote LinkRouter for the new useLink() API but never re-wired the styling props to an actual MUI component.

Fix

Wrap the content in MUI's real Link (component="span" to avoid nesting two <a> tags, same precaution as #7428):

const LinkRouter = (props: LinkProps & { to?: string }) => {
  const { to, children, ...restProps } = props;
  return (
    <Link to={to || ""}>
      <MuiLink component="span" {...restProps}>
        {children}
      </MuiLink>
    </Link>
  );
};

Test added

packages/mui/src/components/breadcrumb/index.spec.tsx asserts the rendered link's inner element carries the MuiLink-root class and that none of sx/underline/color/variant leak through as literal DOM attributes.

Checklist

• Reproduced the bug
• Verified the fix resolves it
• Added a changeset
• Added a regression test
• Existing tests pass (pnpm test in packages/mui — 420 passed, 4 pre-existing/unrelated failures: timezone-dependent DateField tests and a flaky useDataGrid timeout, neither touched by this change)

[changeset-bot]

🦋 Changeset detected

Latest commit: a655fd4

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