fix(button): forward __next__ Button ref to DOM element

[tamas-sage]

Proposed behaviour

Button/next now forwards its ref to the underlying DOM element (button / a) instead of exposing an imperative handle.
This aligns with Dialog/FocusTrap expectations for focusFirstElement and prevents the runtime error when opening the dialog.

Current behaviour

Button/next exposed an imperative handle (focusButton) via ref.
When this was passed to focusFirstElement, FocusTrap expected an HTMLElement-compatible value and opening the dialog could throw a “failed to execute” error.

Checklist

• Commits follow our style guide
• Related issues linked in commit messages if required
• Screenshots are included in the PR if useful
• All themes are supported if required
• Unit tests added or updated if required
• Playwright automation tests added or updated if required
• Storybook added or updated if required
• Translations added or updated (including creating or amending translation keys table in storybook) if required
• Typescript d.ts file added or updated if required
• Related docs have been updated if required

QA

• Tested in provided StackBlitz sandbox/Storybook
• Add new Playwright test coverage if required
• Carbon implementation matches Design System/designs
• UI Tests GitHub check reviewed if required

Additional context

Testing instructions

[edleeks87]

@tamas-sage, apologies the ticket hasn't captured the change to the requirements here. I think a better approach is to make a breaking change on the next button and change the ref to point to the underlying DOM element instead of the handle it has currently. Happy to chat on slack if you want to ping me and we can update the ticket if needed

[tamas-sage]

@tamas-sage, apologies the ticket hasn't captured the change to the requirements here. I think a better approach is to make a breaking change on the next button and change the ref to point to the underlying DOM element instead of the handle it has currently. Happy to chat on slack if you want to ping me and we can update the ticket if needed

Thanks, that makes sense, I’ve updated this PR to use a breaking change on next Button so the ref now points to the underlying DOM element (instead of an imperative handle). I’ve also updated the PR description/title to reflect that.

[edleeks87]

Nice one @tamas-sage, when we merge we should squash/rebase so just this commit and its message is left. We'll also need to add the BREAKING CHANGE comment to the commit so we trigger a major release etc