feat: replace notification checkboxes with card-based layout (#5421)

Replace EventBusCheckboxes with card-based notification settings:
- Each event group gets its own card with responsive grid layout
- Master checkbox per group with indeterminate state
- Inline parameter inputs (CPU threshold) appear when enabled
- Theme-adaptive via Ant Design Card component

Components:
- NotificationLayout, NotificationCard, NotificationHeader, NotificationEvent
- TelegramNotifications, EmailNotifications with explicit event configs

frontend/src/components/ui/notifications/index.ts

@@ -0,0 +1,8 @@
+export type { NotificationEventConfig, NotificationGroupConfig } from './types';
+export { NotificationLayout } from './NotificationLayout';
+export { NotificationCard } from './NotificationCard';
+export { NotificationHeader } from './NotificationHeader';
+export { NotificationEvent } from './NotificationEvent';
+export { NotificationGroup } from './NotificationGroup';
+export { TelegramNotifications } from './TelegramNotifications';
+export { EmailNotifications } from './EmailNotifications';