feat(ui): add toasts for create edit and run flows

- add global ToastProvider and useToast hook mounted at app root

- show success/error toasts for environment, credential, snippet, and scenario create/edit actions

- show run-started/error toasts on scenario run actions with 100ms exit animation

client/src/ui/index.ts

@@ -27,6 +27,9 @@ export type { BreadcrumbsProps, BreadcrumbItem } from './Breadcrumbs/Breadcrumbs
 
 export { ThemeSwitcher } from './ThemeSwitcher/ThemeSwitcher';
 
+export { ToastProvider, useToast } from './Toast/ToastProvider';
+export type { ToastProviderProps } from './Toast/ToastProvider';
+
 export { Timestamp } from './Timestamp/Timestamp';
 export type { TimestampProps } from './Timestamp/Timestamp';