* Replaced the handmade collapse/expand div with Semi UI `<Button>`
* Uses `theme="outline"` and `type="tertiary"` for outlined style
* Shows icon + text when sidebar is expanded, icon-only when collapsed
* Added `iconOnly` prop and dynamic padding to remove extra text area in collapsed state
* Ensured full-width layout with consistent padding for both states
* Updated imports to include `Button` from `@douyinfe/semi-ui`
* Maintains tooltip content for accessibility and better UX
