Danny White be01b38118 docs(design-system): document split button with dropdown pattern (#47422) ...

## Summary
- Add `button-split-dropdown` and `admonition-button-split`
design-system examples for primary action + chevron menu.
- Document the shared middle border pattern (`-ml-px`, `hover:z-10`;
avoid `border-l-0`) in Button and Admonition docs.
- Mirrors the approach established in the custom SMTP email templates
admonition.

## Test plan
- [ ] Open design-system site and verify `Button → Split with dropdown`
preview renders correctly
- [ ] Open `Admonition → Split button with dropdown` preview and confirm
middle border looks correct on hover/focus
- [ ] Confirm peek code shows the documented class names

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added new split-button dropdown live demos, including
icon/chevron-triggered menus with actionable items.
* Added an admonition demo demonstrating a split primary button plus
dropdown trigger with responsive layout.

* **Documentation**
* Expanded “Split with dropdown” guidance with pairing/when-to-use
rules, required styling/border behavior, and responsive layout
instructions for the primary + chevron actions.
* Updated button documentation heading capitalization to match
typography standards.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

2026-07-03 10:14:12 +10:00

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docs

docs(design-system): document split button with dropdown pattern (#47422)

2026-07-03 10:14:12 +10:00