```text
   feat(settings): add notification controls

   - let admins toggle and test Sonner, email, and Reverb delivery
     from one settings screen
   - stop header appearance sync from failing with 419 by sending the
     expected CSRF/XSRF headers
   - redirect stray GETs from the PATCH-only appearance sync endpoint
     to avoid runtime errors
   - restore success toasts after user create and update flows
 ```