When dismiss() was called on a persistent+shaking toast, the .shake CSS
rule (declared after .hiding) overrode toast-out animation. If shake had
already finished, no animationend fired and the element was never removed.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Add showToast() utility in api.js and a matching toast stylesheet.
apiFetch now automatically shows a toast for any 400+ response before
re-throwing, so callers can still .catch() for additional handling.
Toasts stack at the bottom-right, auto-dismiss after 4s, and support
error/warning/success/info levels via a left-border colour accent.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>