Add a useToast() composable + a single ToastHost mounted in AppLayout. Convert
every alert() across views/components (29 call sites, all error paths) to
toast.error, and use toast.success to confirm a warranty refresh. Kills the
native "localhost says" dialog and gives consistent, dismissable feedback.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
