All copy buttons inside `.code-example` blocks now use `.btn-icon.btn-icon-sm`
with a Phosphor `ph-copy` icon instead of the old text-based `.code-example-copy`.

Updated `code-examples.js` to swap the icon to `ph-check` for 1.2 s after copy,
matching the behaviour of `GnCopyButton`.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>