feat: add error message and expandable metadata to notification items

- Show notification.message in notification-item.tsx
- Add Details toggle to expand metadata (exit_code, previous_status, etc.)
- Add CSS styles for message and metadata display

Quality gates: tsc --noEmit pass, 80/80 tests pass

apps/web/src/components/features/notification/notification-item.tsx

@@ -41,7 +41,7 @@ export function NotificationItem({
 
 	const hasDetails =
 		!!notification.message ||
-			Object.keys(notification.metadata || {}).length > 0;
+		Object.keys(notification.metadata || {}).length > 0;
 
 	return (
 		<li

apps/web/src/styles/utilities.css

@@ -2576,4 +2576,3 @@ a:active,
 		transform: translateX(100%);
 	}
 }
-