improvement: updated toasts. no invisible toast anymore.

.cursor/rules/frontend-components.mdc

@@ -40,6 +40,12 @@ Reference: `app/.../treatment/page.tsx` + `components/ui/treatment/TreatmentWork
 - API clients: `lib/api/`.
 - Catch blocks: `getUserFacingError(err, tErrors, fallback)` from `components/shared/formatApiError.ts`.
 
+## Toasts
+
+- Use `useToast()` for transient page feedback — rendered globally by `ToastProvider` in dashboard layout (fixed bottom, above dialogs).
+- Do **not** add `<ToastStack />` inside pages or dialogs.
+- Form/dialog validation: inline error text near the field or submit button, not a toast.
+
 ## When adding UI
 
 1. Check `components/ui/shared/` for an existing primitive.