Adopt toggle controls for diff panel and header button

- add reusable `ui/toggle` and `ui/toggle-group` components built on Base UI
- switch diff view mode controls and chat header diff toggle to use the new toggle primitives
3a5cd89ef2Julius Marminge committed on 2/18/2026, 9:09:33 AMparented25338
4 files changedLine totals unavailable